Add tempest test to check that all datasources expose tables

All datasources should expose tables. If they don't there is obviously
a problem. Adding a simple test for this would be useful to help catch bugs.

Change-Id: Ifa3048863f832a9d0af0f1caf0a755ca88e8f04d
Closes-bug: 1399002
Merge "Add tempest test to check that all datasources expose tables"