ceph_ctl: allow bootstrap to be optional

Signed-off-by: Dan Mick <dan.mick@redhat.com>
ceph_ctl: make get_service_fqdns search for servers with given role

Signed-off-by: Dan Mick <dan.mick@redhat.com>
ceph_ctl: use new get_service_fqdns

Reimplement get_server_fqdns and _get_admin_node() to use the
new get_service_fqdns (_get_admin_node now returns the first target
that has a role of type 'mon')

Signed-off-by: Dan Mick <dan.mick@redhat.com>
ceph_ctl: remove 'only three hosts' test from ExternalCephCtl

Signed-off-by: Dan Mick <dan.mick@redhat.com>