Make dict.keys() PY3 compatible

The dict.keys()[0] will raise a TypeError in PY3,
as dict.keys() doesn't return a list any more in PY3
but a view of list.

Change-Id: I5d8dead560acd897213e785d6eb0bc75a584af1b
Closes-Bug: #1583419

manilaclient/tests/functional/test_shares_metadata.py

@@ -136,7 +136,7 @@ class SharesMetadataReadWriteTest(base.BaseTestCase):
         get = self.user_client.get_share_metadata(self.share["id"])
 
         # Verify share metadata
-        key = metadata.keys()[0]
+        key = list(metadata.keys())[0]
         self.assertIn(key, get)
         self.assertEqual(metadata[key], get[key])