Description of problem:
The VGs named "docker" will be removed by "uninstall.yml" playbooks.
It needs the warning on the document or release notes because someone who was used OCPv3.7 or below one does not expect the VG will removed. 

Additionally, I think the detected conditions which remove docker storage VGs need to be more specific conditions. When the docker storage named other something not included docker string, it's not removed and having potential risks that remove the other one not to related Docker storage VGs. Such as other system and OS VGs included "docker" string into the ones.


Version-Release number of the following components:
rpm -q openshift-ansible

  openshift-ansible-3.9.14-1.git.3.c62bc34.el7.noarch

rpm -q ansible

  ansible-2.4.3.0-1.el7ae.noarch

ansible --version

  ansible 2.4.3.0
    config file = /etc/ansible/ansible.cfg
    configured module search path = [u'/root/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
    ansible python module location = /usr/lib/python2.7/site-packages/ansible
    executable location = /usr/bin/ansible
    python version = 2.7.5 (default, May  3 2017, 07:55:04) [GCC 4.8.5 20150623 (Red Hat 4.8.5-14)]


How reproducible:

Steps to Reproduce:
1. run "/usr/share/ansible/openshift-ansible/playbooks/adhoc/uninstall.yml" after installing OCPv3.9 configured the docker storage setup.
2.
3.

Actual results:
Please include the entire output from the last TASK line through the end of output if an error is generated


When OCP redeploy after uninstall.yml, the installation will be failed.

~~~
Failure summary:

  1. Hosts:    10.0.0.1, 10.0.0.2, 10.0.0.3
     Play:     OpenShift Health Checks
     Task:     Run health checks (install) - EL
     Message:  One or more checks failed
     Details:  check "docker_storage":
               Docker storage drivers 'overlay' and 'overlay2' are only supported with
               'xfs' as the backing storage, but this host's storage is type 'extfs'.
~~~


Expected results:

If this function is new feature, we need to notice it, and warn the uninstall.yml will remove the existing docker VGs and explain the condition which select the VGs included the "docker" on the name for review the system before uninstall.

Additional info:
Please attach logs from ansible-playbook with the -vvv flag