Extract getting instance's AZ into a helper module.

An instance's availability zone logic may used by many modules,
so move it from extend API into helper module `nova.availability_zones`.
Also add some tests for the new method.

part of bp: different-availability-zone-filter

Change-Id: I5916a0b09d5dddec338e8e36503953720dfd6bcd
Refactor nova.volume.cinder.API to reduce roundtrips with Cinder

Make cinder.API methods accept volume_id instead of the whole volume object.
This will remove redundant roundtrip to get the volume before
passing it to other methods as in fact they only need the id.

Fixes bug 1172297

Change-Id: I5e7f944c1c29b2f211ece2ef86c0959c81e806df
Merge "Extract getting instance's AZ into a helper module."
Merge "Refactor nova.volume.cinder.API to reduce roundtrips with Cinder"
Merge remote-tracking branch 'm_src_repo/citrix-fixes' into build-temp