Deprecate `.image.glance` in favor of glanceclient

Nova currently maintains a wrapper on top of glanceclient which is both
old and ugly. This spec proposes getting rid of that code in favor of
using just glanceclient in order to reduce the code needed to be
maintained by the nova team, allow the glance team to move forward more
easily and allow nova for better supporting glance's API v2.

Change-Id: I1a86fcf3f2321f2b16b8787faecd099d80c1e3c4
Merge "Deprecate `.image.glance` in favor of glanceclient"