Add basic HookSpecificCheck coverage

Not testing the git-specific (e.g. staged files) stuff yet, but sanity
checking commit messages.

Change-Id: I07298d2615365796906c37b8f6d469a78840f0ec
Reviewed-on: https://gerrit.causes.com/22959
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Joe Lencioni <joe.lencioni@causes.com>