docs: Document how to revert, confirm a cold migration
docs: Document how to revert, confirm a cold migration

This relies on the recently added 'openstack server migrate confirm' and
'openstack server migrate revert' commands.

Change-Id: I58d0a62aeeb4bb23a7ed3a8e9fe5ddb7f2dd3877
Signed-off-by: Stephen Finucane <492121341a95b3c3aab646bed44634f739dd019b@redhat.com>
Depends-On: I0cb6304c794bffaec785add9f7b8cf53ab28cacd

openstack/nova,mahak/nova,klmitch/nova,rahulunair/nova,klmitch/nova,rahulunair/nova,klmitch/nova,klmitch/nova,openstack/nova,mahak/nova,openstack/nova,mahak/nova,rahulunair/nova