Currently, doing a cold migration while specifying a target host is not
possible however nova api supports it since version 2.56.
This patch allows passing "--host" when doing a cold migration.
It runs normally if --os-compute-api-version is 2.56 or greater and
returns an error otherwise.
Change-Id: I960109008096ce8bb4e4c8ca6ffb22c33aacd995
Story: 2003325
Task: 24359