Fix int-tests for different datastores

Reasons:
 - Integration tests are failing with any other
   datastore rather than mysql.
Changes:
 - `dbaas_datastore` added to test_begin.conf
 - `dbaas_datastore_version` added to test_begin.conf
 - while kick-start setting `dbaas_datastore`
  and dbaas_datastore_version` to test.conf

Closes-Bug: #1328557