Implement scheduler hints for APIv2

We've done this implementation because we need to use scheduler hint in
cinder with some specific filters. So, most part of code have been
imported from nova.

bp scheduler-hints
docimpact

Change-Id: Ib7e858e98110a30c5f8d5ff05d03ce2d61f04f92
Merge "Implement scheduler hints for APIv2"