Added exec option in rh-ceph-ansible task and balancer commands on system tests

[sunilkumarn417]

Signed-off-by: sunilkumarn417 sunnagar@redhat.com

• Added exec option in rh-ceph-ansible task.
• Added balancer commands on system tests to overcome full OSD issue.

[sunilkumarn417]

http://pulpito.ceph.redhat.com/sunnagar-2020-08-21_13:01:35-smoke:ceph-ansible-master-distro-basic-clara/