Add instruction to run a short test to validate the setup.
Add instruction to run a short test to validate the setup.

Update README with instruction to run a short test to validate
the setup before running a full API test.

Change-Id: I35ebc8b3875602bf41d5b8af243311bc98a41f1e

stackforge/refstack-client,openstack/refstack-client,stackforge/refstack-client,openstack/refstack-client