tests: Add monkey patching class decorator

Using the new MonkeyClass decorator, you can do monkey patching during
all test methods in a test case class, without implementing setUp() or
tearDown().

Change-Id: Ice429b01afaf00730ff59dcdf866ab5eeae6b926
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/20175
Reviewed-by: Alon Bar-Lev <alonbl@redhat.com>
Reviewed-by: Allon Mureinik <amureini@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>