Group should only return its own variables

Otherwise, a host in two groups, A and B, using a variable defined
in group A and all will get the value of all, as B's variables will
include the all variable.

Partially fixes #1647.

lib/ansible/inventory/group.py

@@ -57,13 +57,7 @@ class Group(object):
         return list(hosts)
 
     def get_variables(self):
-
-        vars = {}
-        # FIXME: verify this variable override order is what we want
-        for ancestor in self.get_ancestors():
-            vars.update(ancestor.get_variables())
-        vars.update(self.vars)
-        return vars
+        return self.vars.copy()
 
     def _get_ancestors(self):