Add image members tests.

This commit adds client methods for the glance v1 api for
interacting with image members. It also adds some basic tests
for creating, getting, and deleting image members.

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

Change-Id: I997ab525c05ed15bfd857b2cfb634379d0b3fec2
Merge "Add image members tests."