Glance client no longer isa http client

If the client has-a http_client, then is must not be an is-a.  This has been tested with the current version of glanceclient and the master branch.

Closes-Bug: #1269821
Change-Id: I14d67eb094bfb4c2dbc07106343488298b6a9409
Python 3: the content of a FakeResponse must be bytes

Encode '_content' if necessary.

Change-Id: I25c1e1cd5330f0519bf062be840045d0ef520b28
Merge "Glance client no longer isa http client"