ceph-infra: open dashboard port on monitor

ceph-infra: open dashboard port on monitor

When there's no mgr group defined in the ansible inventory then the
mgrs are deployed implicitly on the mons nodes.
If the dashboard is enabled then we need to open the dashboard port on
the node that is running the ceph mgr process (mgr or mon).
The current code only allow to open that port on the mgr nodes when they
are present explicitly in the inventory but not implicitly.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1783520
Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>