shrink-mon: search mon in the quorum_names list

shrink-mon: search mon in the quorum_names list

If we're looking at the mon hostname in the ceph status output then
there's some scenarios where this could be true.
If we collocate some services (mons, mgrs, etc..) then the hostname of
the monitor to shrink will still be present in the ceph status (like
in mgrs or other).
Instead we should check the hostame only in the mon part of the output.

Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>
(cherry picked from commit 734c0dc3106a14a0bacd952d1fd91e3d8856bac6)