Multiple API version support

* Use multiple entry point groups to represent each API+version
  combination supported
* Add some tests

Try it out:
* Right now only '* user' commands have multiple overlapping versions;
  you can see the selection between v2.0 and v3 by looking at the
  command help output for 'tenant' vs 'project':

  os --os-identity-api-version=2.0 help set user
  os --os-identity-api-version=3 help set user

Change-Id: I7114fd246843df0243d354a7cce697810bb7de62

1 files changed, 1 insertions, 1 deletions

diff --git a/HACKING b/HACKING
index e9bcb7ea..dd31ccd5 100644
--- a/HACKING
+++ b/HACKING
@@ -39,8 +39,8 @@ Human Alphabetical Order Examples
   import logging
   import random
   import StringIO
+  import testtools
   import time
-  import unittest
 
   from nova import flags
   from nova import test