Fix v2 qos-key command

As part of commit 0d2bf657ae,
qos-key command's v2 support got broken again reintroducing
bug #1284321.

Change-Id: I30d60b060bd1b161bc96c4a529f4732b9ceef90d
Closes-Bug: 1284321

cinderclient/v2/shell.py

@@ -1942,6 +1942,7 @@ def do_qos_disassociate_all(cs, args):
            default=[],
            help='Metadata key and value pair to set or unset. '
                 'For unset, specify only the key.')
+@utils.service_type('volumev2')
 def do_qos_key(cs, args):
     """Sets or unsets specifications for a qos spec."""
     keypair = _extract_metadata(args)