restapi : --parent-tag-id option doesn't exists in 'update tag' options (#1006905)

update tag does not display --parent-tag-id on
pressing tab as one of the valid options

Change-Id: I7c439521bb8432dd4d9f3ed52b1dd24a9bfc3712
Bug-Url: https://bugzilla.redhat.com/1006905
Signed-off-by: Ravi Nori <rnori@redhat.com>