Add the gifn-apply test tool

Add a tool that checks out the repositories mentioned in
a git-if-needed patch series, runs gif-it-needed, and performs
some checks on its operation. This tool will eventually be used in
a Zuul test job for this repository.

Change-Id: Id02fb7c21f5ab34d9639bf845fcc3961d929b13b
26 files changed
tree: 37e74bf5a109ab2625982730a5371bb486337a0e
  1. .gitreview
  2. patches/
  3. tools/