Check common.keyring is provided before check common.keyring.admin key

Related-Prod: PROD-36064
Change-Id: I7bd3c3693102e9195ae288cdf4aa57a2a1fcc29c
diff --git a/ceph/mon.sls b/ceph/mon.sls
index b660cdf..db172b9 100644
--- a/ceph/mon.sls
+++ b/ceph/mon.sls
@@ -54,7 +54,7 @@
     - pkg: mon_packages
     - file: common_config
 
-{%- if common.keyring.admin is not defined %}
+{%- if common.get('keyring', {}).admin is not defined %}
 /var/lib/ceph/mon/{{ common.get('cluster_name', 'ceph') }}-{{ grains.host }}/keyring:
   file.managed:
   - source: salt://ceph/files/mon_keyring