ceph-facts: only get fsid when monitor are present

ceph-facts: only get fsid when monitor are present

When running the rolling_update playbook with an inventory without
monitor nodes defined (like external scenario) then we can't retrieve
the cluster fsid from the running monitor.
In this scenario we have to pass this information manually (group_vars
or host_vars).

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1877426
Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>