In the process of unification of the clients code we should use
composition to allow easier replacement with common HTTPClient.
Related to blueprint common-client-library-2
Change-Id: I5addc38eb2e2dd0be91b566fda7c0d81787ffa75
Add unittests for the following modules:
* glanceclient.shell
* glanceclient.v1.shell
* glanceclient.v1.legacy_shell
* glanceclient.v2.shell
Also add mock library to the tools/test-requires
Implements: blueprint glanceclient-shells-unittests
Change-Id: I5ec527c5efff3726932d234d7c67e08149643f89