Use tenant name and user name for user id

Currently, swift3 abuses an access key as a S3 user id, which is not human
readable string in the case of keystone auth.  Let's use the following form:

  [tenant name]:[user name]

This is the same format as what the tempauth middleware uses.

Change-Id: I026bd28f0be81a38be515276c1dab532dcff7130
Merge "Use tenant name and user name for user id"