Fixing bug in which playbook vars were not merged properly

This occurred when a hash would be passed in via extra args and the
hash variable behavior was set to 'merge', which resulted in the
variable from extra args replacing the playbook variable.

lib/ansible/playbook/play.py

@@ -649,7 +649,7 @@ class Play(object):
             raise errors.AnsibleError("'vars_prompt' section is malformed, see docs")
 
         if type(self.playbook.extra_vars) == dict:
-            vars.update(self.playbook.extra_vars)
+            vars = utils.combine_vars(vars, self.playbook.extra_vars)
 
         return vars