Adding ability to set up optional groups for user.

Change-Id: I0109e9b5298253fac0dac090066c313e8f7fccbb
diff --git a/tests/pillar/system.sls b/tests/pillar/system.sls
index de1da29..6a0b16b 100644
--- a/tests/pillar/system.sls
+++ b/tests/pillar/system.sls
@@ -141,6 +141,8 @@
         groups:
           - db-ops
           - salt-ops
+        optional_groups:
+        - docker
       salt_user1:
         enabled: true
         name: saltuser1