Datasource driver load error not properly handled

[Tim Hinrichs]

In congress/managers/datasource.py, in the add_datasource method, we call

                cage.createservice(name=datasource['name'],
                                   moduleName=driver_info['module'],
                                   args=datasource['config'],
                                   module_driver=True)

without catching the possible DataServiceError that this method throws. If it throws a DataServiceError, we should call

                    engine.delete_policy(datasource['name'])

and then reraise the error.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/169581

[OpenStack Infra (hudson-openstack)]

Change abandoned by Tim Hinrichs (<email address hidden>) on branch: master
Review: https://review.openstack.org/169581
Reason: This was a good change, but it didn't get merged b/c of a merge conflict for long enough that someone else fixed the same bug in a separate changeset.