Add expected fails to unit tests

When was the last time you tested webodf/tests/ops/failingtests.xml ?
Right.
Better to have testing of the so far failing tests in the normal builds, to see automatically when they no longer fail.

Also helps with TDD, when you create your tests in advance knowing which one will fail.

With these patches so far only used with the operationstests.xml, where failing tests can be marked with an attribute isFailing="true".