Add help for purge_deleted command age argument

At a bare minimum explaining this argument helps understand what
purge_deleted is going to do.

Change-Id: If73ba272e8ea0742f8be93994ec2fac68d4ed3fd
Fix RequestContext.to_dict user/username inconsistency

The username value should be returned, not the self.user value,
otherwise you unexpectedly get inconsistent results if you ever
override the username after creating the object.  Some tests
added, one of which illustrates the problem.

Change-Id: I95e416e3046607d8b0406812705949e8ff464f86
Closes-Bug: #1237459
Add cinder prop image, deprecate imageRef

This change does a lookup on the provided image so that
an image name or UUID can be specified in the property.

imageRef has been documented as being deprecated.

Closes-Bug: #1234263
Change-Id: I95190e3f53ddac8eb41306b7003aa93e75886eb7
Merge "Fix RequestContext.to_dict user/username inconsistency"
Merge "Add cinder prop image, deprecate imageRef"
Merge "Add help for purge_deleted command age argument"