Fix comment on `repo_path`

This was made a generic method and is no longer specific to targeting
`.githooks`.

Change-Id: I2c9b0c4fa3027b4e7c735ef3a07f683ff6f7c689
Reviewed-on: https://gerrit.causes.com/22727
Tested-by: Aiden Scandella <aiden@causes.com>
Reviewed-by: Joe Lencioni <joe.lencioni@causes.com>
Add back modified_files helper

It's useful to DRY things up in hook-specific checks.

Change-Id: Ic9e48ce48e7c423e07800e98ef5d1768a2faa55c
Reviewed-on: https://gerrit.causes.com/22738
Tested-by: Aiden Scandella <aiden@causes.com>
Reviewed-by: Joe Lencioni <joe.lencioni@causes.com>
Read repo-specific overcommit.yml configuration

As written by the installer, this file currently contains a set of
'excludes' which exclude Causes/Gerrit-specific hooks from being run.

Change-Id: Ie4878ce8de2ade2f0e0a68acebd45b9a519c03f5
Reviewed-on: https://gerrit.causes.com/22748
Tested-by: Aiden Scandella <aiden@causes.com>
Reviewed-by: Joe Lencioni <joe.lencioni@causes.com>