Fix "openstack image unset" command's help message typo

Change-Id: Ie286d9ee6054cc2126473d7e6e77bafbfd80023b
Closes-Bug: #1712473

Author: lihaijing

openstackclient/image/v2/image.py

@@ -990,7 +990,7 @@ def get_parser(self, prog_name):
             default=[],
             action='append',
             help=_("Unset a tag on this image "
-                   "(repeat option to set multiple tags)"),
+                   "(repeat option to unset multiple tags)"),
         )
         parser.add_argument(
             "--property",
@@ -999,7 +999,7 @@ def get_parser(self, prog_name):
             default=[],
             action='append',
             help=_("Unset a property on this image "
-                   "(repeat option to set multiple properties)"),
+                   "(repeat option to unset multiple properties)"),
         )
         return parser