Now the os-evacuate API supports a new body argument called 'force' which
helps the operators to bypass the scheduler call in case they provide a host.
Also modifies the host_evacuate helper method in the contrib tree to make sure
operators also have the force flag in case they need it for a global call.
Change-Id: I5272e9809a7d8be482e87548c6a3b11186c5d1e1
Partially-Implements: blueprint check-destination-on-migrations-newton
1aa042e0cb