Add the ability to run a new project created hook

Notify users when a new project has been created. This could solve
an issue in the Jenkins gerrit-trigger-plugin where we need to
continuously fetch the whole project list (using the command
gerrit ls-projects) to get project name auto completion working
in the Project Configuration pages. By letting the plug-in pickup
new projects on the fly, our auto completion would be up-to-date
much quicker and also drain less resources from Gerrit.

The hook takes the following form:

project-created --project <project name> --head <head name>

Change-Id: Ibf53946b12df4efd2f929fa7fc6d23499ed7ed88
8 files changed