fix meta/salt with missing pillar

Change-Id: Ie4d666a97638f84b53023e1e4aa88f8c925921ba
diff --git a/mysql/meta/salt.yml b/mysql/meta/salt.yml
index acd8891..dc1a9ec 100644
--- a/mysql/meta/salt.yml
+++ b/mysql/meta/salt.yml
@@ -1,5 +1,5 @@
 minion:
-  {%- if pillar.mysql.server is defined %}
+  {%- if pillar.get('mysql', {}).get('server') %}
   mysql:
     {%- from "mysql/map.jinja" import server with context %}
     mysql.unix_socket: /var/run/mysqld/mysqld.sock