3.0 travis fixes

This fixes random fails in sqlite, some of the errors fixed:

* Test suites can be nested in PHPUnit, we were dropping fixtures even though the parent suite was not over
* Dropping tables in between tests methods was not actually required, removing it made the test suite a bit faster and more robust
* A test in ConnectionTest was re-creating the sqlite connection, effectively dropping all tables. I had to remove this test entirely and will look into adding it back at a later point.
* Sqlite does not like leaving cursors open, added `closeCursor` calls in the ConnectionTest suite.