Exclude guardian-xenial when running tests
Exclude guardian-xenial when running tests

Xenial is now default and we do not have xenial-specific scripts
anymore.
Also, make `./sctripts/test -a` panes aligned perfectly to please my OCD-self

[#161616344]

cloudfoundry-incubator/guardian-release,cloudfoundry-incubator/guardian-release,cloudfoundry-incubator/guardian-release