Eliminate the impact of "wait_until='BUILD'"

BUILD is just a middle state within a short period of time.
It's suspended and unstable when creating a server,
and it will be ACTIVE eventually if everything is ok.

But many places uses the wait_until='BUILD' to create server.
resp, server = cls.create_server(image_id=cls.image_ref,
                                   flavor=cls.flavor_ref,
                                   wait_until='BUILD')

In this patch I add following code in wait_for_server_status
method instead of deleting those incorrect usage.
Thus will use the smallest change
to support BUILD state for wait_until as well.

if status == 'BUILD' and server_status != 'UNKNOWN':
            return

Change-Id: I146fdff56af29ae0aef9b5cff8bcea5468ff595c
Closes-Bug: #1214202
Merge "Eliminate the impact of "wait_until='BUILD'""