mon: do not create unnecessarily mgr keyrings
mon: do not create unnecessarily mgr keyrings

there's no need to generate mgr keyrings 'mgr.monX' when mgrs aren't
collocated with monitors.

Signed-off-by: Guillaume Abrioux <30a9df5a0293a6108675377fa1673f7aa713f915@redhat.com>

ceph/ceph-ansible,ceph/ceph-ansible