Remove Brick iser dependency on cinder

This patch removes the brick iser.py's dependency
on cinder exceptions and volume_utils.
This required moving some exceptions out of cinder's
exception.py that the iser.py raises.  Also had
to create a BrickException and refactor existing
brick exceptions to use the new BrickException model.

Fixes Bug #1210312

Change-Id: I672375807fed4952e5321fbcd9b57b9ef369f68f
Merge "Remove Brick iser dependency on cinder"