Add retry for salt.minion.cert state

Change-Id: Iff73ecf946684edb1d1de23b49f03ad61a61d730
diff --git a/tcp_tests/templates/shared-core.yaml b/tcp_tests/templates/shared-core.yaml
index ae47e03..3b1a716 100644
--- a/tcp_tests/templates/shared-core.yaml
+++ b/tcp_tests/templates/shared-core.yaml
@@ -192,7 +192,7 @@
   cmd: salt --hard-crash --state-output=mixed --state-verbose=False
     -C 'I@nginx:server' state.sls salt.minion.cert
   node_name: {{ HOSTNAME_CFG01 }}
-  retry: {count: 1, delay: 15}
+  retry: {count: 3, delay: 15}
   skip_fail: false
 
 - description: Install nginx server