dashboard: run dashboard role on mgr/mon nodes
dashboard: run dashboard role on mgr/mon nodes

We don't need to execute the ceph-dashboard role on the nodes present
in the grafana-server group. This one is dedicated to the grafana and
prometheus stack.
The ceph-dashboard needs to executed where the ceph-mgr is running. It
is either on the dedicated mgr nodes or if mgr and mon are collocated
implicitly on the mon nodes.

Signed-off-by: Dimitri Savineau <a50a620e679eed14f4e99998b821cea8884cf228@redhat.com>

ceph/ceph-ansible,ceph/ceph-ansible