ceph-volume/tests: set ANSIBLE_CONFIG env var

ceph-volume/tests: set ANSIBLE_CONFIG env var

Without loading the ansible.cfg file from ceph-ansible project, we don't
have the pipelining enabled which can result in significant performance
improvement.
This removes the ANSIBLE_ACTION_PLUGINS, ANSIBLE_RETRY_FILES_ENABLED and
ANSIBLE_SSH_RETRIES environment variables as it is already included in the
ansible.cfg file.

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>
(cherry picked from commit b758fdd829e3b4d7b790e6d35a02c97f3962d13e)