Relax OpenStack upper capping of client versions

- uncap keystoneclient and bump to >=0.3.0 to match requirements
- fix test case to handle change in keystoneclient where cached
values are stored as string now. Previous test passed in tuple and
new auth_token would fail when it tried to json.loads the
tuple. (see _cache_get() in keystone auth_token)

Change-Id: I568d8e0ae6586b91d5e38cb8750731f3fe6e22e7
Fixes:Bug#1200214