Add support for skipping all modes of a single test...

...with 'python tests/runner.py skip:ALL.test_freetype', instead of having to specify all the modes for the test to be skipped by hand.

A common way the buildbots break is that a new test mode is added, but the set of skipped tests is specified manually for each test mode type, and the new test mode is then not skipped, but executed and resulting in failure. This allows setting up the skipped tests list so that it skips certain tests even if there are new test modes added.