Description of problem:
OVN migration tool playbooks do not seem to be properly ported to RHEL8 and it fails issuing docker commands where it should be podman.

Version-Release number of selected component (if applicable):
16.1
python3-networking-ovn-migration-tool-7.2.1-0.20200611111150.18fabca.el8ost.noarch


How reproducible:
always

Steps to Reproduce:
1. Follow https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/16.1-beta/html/networking_with_open_virtual_network/migrating-ml2ovs-to-ovn
2. Execute step 3.2.11 - ovn_migration.sh setup-mtu-t1
3.

Actual results:
Playbook bails out trying to execute docker restart on a controller

Expected results:
Playbook should succeed

Additional info:

(overcloud) [stack@undercloud ~]$ ovn_migration.sh setup-mtu-t1                                                                                            
ansible-playbook 2.9.10                                                                                                                                    
  config file = /home/stack/ansible.cfg                                                                                                                    
  configured module search path = ['/home/stack/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']                                           
  ansible python module location = /usr/lib/python3.6/site-packages/ansible                                                                                
  executable location = /usr/bin/ansible-playbook                                                                                                          
  python version = 3.6.8 (default, Dec  5 2019, 15:45:45) [GCC 8.3.1 20191121 (Red Hat 8.3.1-5)]                                                           
Using /home/stack/ansible.cfg as config file                                                                                                               
[WARNING]: Invalid characters were found in group names but not replaced, use -vvvv to see details                                                         
                                                                                                                                                          
PLAYBOOK: reduce-dhcp-renewal-time.yml ********************************************************************************************************************
1 plays in /home/stack/playbooks/reduce-dhcp-renewal-time.yml
                                                                                                                                                           
PLAY [overcloud-controllers] ******************************************************************************************************************************
                                                          
TASK [Gathering Facts] ************************************************************************************************************************************
task path: /home/stack/playbooks/reduce-dhcp-renewal-time.yml:3                                                                                            
Thursday 09 July 2020  12:13:08 -0400 (0:00:00.086)       0:00:00.086 *********             
[DEPRECATION WARNING]: Distribution redhat 8.2 on host overcloud-controller-0 should use /usr/libexec/platform-python, but is using /usr/bin/python for 
backward compatibility with prior Ansible releases. A future Ansible release will default to using the discovered platform python for this host. See 
https://docs.ansible.com/ansible/2.9/reference_appendices/interpreter_discovery.html for more information. This feature will be removed in version 2.12. 
Deprecation warnings can be disabled by setting deprecation_warnings=False in ansible.cfg.     

ok: [overcloud-controller-0]                                                                                                                               
META: ran handlers                                                                                                                                         
                                                                                                                                                           
TASK [Update dhcp_agent configuration file option 'dhcp_renewal_time'] ************************************************************************************
task path: /home/stack/playbooks/reduce-dhcp-renewal-time.yml:5                                                                                            
Thursday 09 July 2020  12:13:12 -0400 (0:00:04.283)       0:00:04.369 *********                                                                            
changed: [overcloud-controller-0] => {"backup_file": "/var/lib/config-data/puppet-generated/neutron/etc/neutron/dhcp_agent.ini.379749.2020-07-09@18:13:14~"
, "changed": true, "gid": 42435, "group": "42435", "mode": "0640", "msg": "option added", "owner": "root", "path": "/var/lib/config-data/puppet-generated/n
eutron/etc/neutron/dhcp_agent.ini", "secontext": "unconfined_u:object_r:container_file_t:s0", "size": 6921, "state": "file", "uid": 0}                     
                                                                                                                                                           
TASK [Get the neutron dhcp agent docker id] ***************************************************************************************************************
task path: /home/stack/playbooks/reduce-dhcp-renewal-time.yml:16                                                                                           
Thursday 09 July 2020  12:13:13 -0400 (0:00:01.015)       0:00:05.385 *********                                                                            
changed: [overcloud-controller-0] => {"changed": true, "cmd": "docker ps | grep neutron_dhcp | awk '{print $1}'", "delta": "0:00:00.008336", "end": "2020-0
7-09 18:13:15.124203", "rc": 0, "start": "2020-07-09 18:13:15.115867", "stderr": "/bin/sh: docker: command not found", "stderr_lines": ["/bin/sh: docker: c
ommand not found"], "stdout": "", "stdout_lines": []}                                                                                                      
                                                                                                                                                           
TASK [Restart neutron dhcp agent] *************************************************************************************************************************
task path: /home/stack/playbooks/reduce-dhcp-renewal-time.yml:22                                                                                           
Thursday 09 July 2020  12:13:14 -0400 (0:00:00.853)       0:00:06.238 *********                                                                           
fatal: [overcloud-controller-0]: FAILED! => {"changed": false, "cmd": "docker restart", "msg": "[Errno 2] No such file or directory: b'docker': b'docker'",
 "rc": 2}                                                
...ignoring                                                                                                                                                
META: ran handlers    
META: ran handlers                                        

PLAY RECAP ************************************************************************************************************************************************
overcloud-controller-0     : ok=4    changed=2    unreachable=0    failed=0    skipped=0    rescued=0    ignored=1   

Thursday 09 July 2020  12:13:14 -0400 (0:00:00.608)       0:00:06.846 *********
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