inventory directory parser: add host to group only once

lib/ansible/inventory/dir.py

@@ -79,6 +79,9 @@ class InventoryDirectory(object):
                         # note: depth numbers on duplicates may be bogus
                         for k, v in host.vars.iteritems():
                             self.hosts[host.name].set_variable(k, v)
+                    # host can already exist from other source (same name,
+                    # different object):
+                    if host.name not in [h.name for h in self.groups[name].hosts]:
                         self.groups[name].add_host(self.hosts[host.name])
 
             # This needs to be a second loop to ensure all the parent groups exist