Add large_ops scenario test

Try spinning up a specific number of instances (set via config) by using
the min_instances option. And make sure all instances go to active
state. Note since the number of instances a cloud can handle is cloud
specific this test is disabled by default.

This can be used in Devstack by using the 'VIRT_DRIVER=fake' option in
devstack.

Change-Id: I30c7d7d113053b47d6dffa6295ad6068810cad32
Test Tokens - V3

Adds test script "test_tokens.py" so as to validate v3 password
authentication for a given user. Support functions are added in
client files in both the interfaces.

Implements: blueprint keystone-tokens-test
Change-Id: I9a810844b1d991f829f411db308e37a02bd6c09e
Merge "Test Tokens - V3"
Merge "Add large_ops scenario test"