Add a unit test to make sure Pegleg only considers YAML files
when linting
Fixes a typo in filename for test_selectable_linting
Changed site_yaml file stucture to more resemble real site
directory structure
Change-Id: Ib1520f9509d279d88b4408858878022fb05c7707
Adds option -x to exclude certain linting policies
and -w to warn of failure for certain linting policies
if failures are expected.
Updates gitignore to exclude files created when running
tests.
Adds requirements for testing.
Adds unit test for new cli options and test
site-definition.yaml
Documentation for cli options can be found here [0].
[0]-https://review.gerrithub.io/#/c/403216/
Change-Id: I6e905c1ba7a23d0b2fdbf9552bec8a6620ff9731