ceph-mon: detect ANSIBLE_ROLES_PATH if present

ceph-mon: detect ANSIBLE_ROLES_PATH if present

Some deployments can't copy infrastructure playbooks outside of the
infrastructure-playbooks directory. Thus they use ANSIBLE_ROLES_PATH to
overcome this. However some roles have 'playbook_dir' hardcoded, which
results in wrong path since the execution comes from
infrastructure-playbooks. Basically the role triggered by a playbook
from infrastructure-playbooks believes that the roles are in
infrastructure-playbooks/roles. This commit fixes that.

Signed-off-by: Sébastien Han <seb@redhat.com>