Hacking checks for negative test cases

This patchset adds 2 hacking checks for making sure negative
tests have correct conventions applied.

* T117: Check that each negative test has the
  ``@decorators.attr(type=['negative'])`` applied

This patch set adds both hacking checks, adds unit tests
and updates HACKING.rst documentation with both new checks.

Closes-Bug: 1781044
Change-Id: I46df351187d22090861150c84fa0a0c1054ae3d6
3 files changed