check-entry-points.py to verify extensions

Wikimedia Jenkins expects extensions to define a PHP entry point named a
like the directory holding the extension, ie:

 Foobar/Foobar.php

This script walk the directories and attempt to find such entry points.
It also reports apparently empty repositories.

Bug: 69247
Change-Id: I27ae748a326db7c9dc462add46dced4b48298ddd
Merge "check-entry-points.py to verify extensions"