don't clean up the test environment if a data provider was finished

endTestSuite() also gets called if a data provider was processed successfully. But in this case we shouldn't clean up the test environment, otherwise all following tests will fail. 

That's just a quick fix, in the long run we should move away from the listeners to a base class for all tests to handle the clean-up and other stuff.

see: https://github.com/owncloud/core/issues/9963

cc @DeepDiver1975 @PVince81