Description of problem:
ansible-playbook must be run using ansible user as it has been suggested to copy ssh-key as ansible user. Running ansible-playbook as root user after copying ssh-key as ansible user will result in denial of permission.

How reproducible:
Always

Steps to Reproduce:
1. Follow docs to configure ceph-ansible to set-up a cluster.
2. Run ansible-playbook as mentioned in Step 5 of 3.2.6 (example)

Given - 

# ansible-playbook site.yml [-u <user_name>]

Appropriate version -

$ ansible-playbook site.yml [-u <user_name>]


Actual results:

TASK [check for python2] ****************************************************************************************************************************************************
fatal: [magna097]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: Warning: Permanently added 'magna097,10.8.128.97' (ECDSA) to the list of known hosts.\r\nPermission denied (publickey,gssapi-keyex,gssapi-with-mic,password).\r\n", "unreachable": true}
 


Expected results:
anisble-playbook must be able to reach all other nodes to carry on expected job.

Additional info:
Same change has to be made in all places where ansible-playbook is expected be used.
Other examples - 
1) step 5, Section 4.1 - Install doc
2) step 3, Section 6.3 - Install doc
3) step 6 in Procedure: Installing Red Hat Ceph Storage as a Container Image by Using Ansible section of 'Deploying Red Hat Ceph Storage 2 as a Container Image' 
4) step 4, Section 6.1.2 - Admin doc
5) step 5, Section 6.3.2 - Admin doc