Fix forgotten agentSh call without class

Change-Id: Ibb277e6b0a3fbd43c93574ffaaa13d612fe060e2
diff --git a/src/com/mirantis/mk/Git.groovy b/src/com/mirantis/mk/Git.groovy
index eccc03e..78d236c 100644
--- a/src/com/mirantis/mk/Git.groovy
+++ b/src/com/mirantis/mk/Git.groovy
@@ -171,7 +171,7 @@
 
         if (pushSource == true) {
             followTagsArg = followTags && pushSourceTags ? "--follow-tags" : ""
-            agentSh "git push ${followTagsArg} origin HEAD:${branch}"
+            ssh.agentSh "git push ${followTagsArg} origin HEAD:${branch}"
         }
     }