Break out RestClient error checking.

This commit breaks out the error checking from the request()
method in RestClient. This allows for the glance_http module
to use the same error checks as RestClient, to keep compatibility
between the 2 modules.

Partially implements blueprint add-glance-api-v1-tests

Change-Id: I0b21c93afcee8e9a22782b12c7b7e1f1ec1ea64c
Add an images client.

This adds support for testing the glance API directly.
We no longer need to use python-glanceclient to run
the images tests.

Fixes bug 1089765
Partially implements blueprint add-glance-api-v1-tests

Change-Id: I404e43e2e6ffecb5131cdcc43df03b8da0e7f0f8
Merge "Break out RestClient error checking."
Merge "Add an images client."