Allow @unittest.expectedFailure on all TestCase methods

TestCase allows test methods to be 'multi-site' tests, which
will be re-run for each site in the TestCase sites matrix.

The metaclass has previously checked that the test method only
has 1 or 2 arguments.  @unittest.expectedFailure replaces the
test method with a decorated version that appears as if it has
zero arguments, due to the way decorators work.  This change
allows test methods with 0 arguments.

Change-Id: Ib6d74af168e0bad93df65da2965daffa6b3951e0
@expectedFailureIf(TRAVIS=true) on imageusage test

Add new @expectedFailureIf to the imageusage test which has been
failing frequently recently, so failure is allowed on TRAVIS, but
not on other test hosts.

Bug: 71971
Change-Id: I0fa7c8cced3b24c8e8914b7f05290b8be2523575
Merge changes I0fa7c8cc,Ib6d74af1

* changes:
  @expectedFailureIf(TRAVIS=true) on imageusage test
  Allow @unittest.expectedFailure on all TestCase methods