Fix exception valid_actions value
Fix exception valid_actions value

While doing zanata translations for tacker,
noticed the exception message was not using correct
valid_actions values due a typo.

Change-Id: I7c62c4dd7c2fdad61f3abd76c3fa563365964256

openstack/tacker,stackforge/tacker,openstack/tacker,stackforge/tacker,openstack/tacker