Enable query image by tag

This patch will enable Glance client to query images by user
defined tags.

Implement bp image-query-by-tag
Implement bp glance-client-v2

Change-Id: I6f54630c5b7c9c567d85485ad4289284e5486814

glanceclient/v2/shell.py

@@ -28,9 +28,11 @@ from glanceclient import exc
            help='Display images owned by <OWNER>.')
 @utils.arg('--checksum', metavar='<CHECKSUM>',
            help='Display images matching the checksum')
+@utils.arg('--tag', metavar='<TAG>', action='append',
+           help="Filter images by an user-defined tag.")
 def do_image_list(gc, args):
     """List images you can access."""
-    filter_keys = ['visibility', 'member_status', 'owner', 'checksum']
+    filter_keys = ['visibility', 'member_status', 'owner', 'checksum', 'tag']
     filter_items = [(key, getattr(args, key)) for key in filter_keys]
     filters = dict([item for item in filter_items if item[1] is not None])