Unit tests can now expect failure

Internal cmockery tests need a method to record
that they expected a certain failure.  Introduced
a new API called unit_test_expect_failure() which
'should' be used only for internal testing.
xUnit report show if unable to run tests - TEST

This commit includes an assert in cmockery to
purposely make the execution of tests fail.  Jenkins
should then pick up the xml files which show the
error and report accordingly.

A commit after this one will remove the assert.