I'm not 100% sure, but I don't see a benefit in allowing people to
override test status from inside test. They are suppose to use
assertions, or `self.fail`-like methods. With this change it'd be harder
to manually override the test status (as can be seen on updated
unittests) but we minimize the accidental write into `self.status`
variable, which can lead to confusing results.

Note we can consider adding `set_status` method to allow setting this
property, but I'd like to avoid allowing direct `self.status = ` usage.
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>