Migrate mediawiki-core-code-coverage to Zuul cloner

zuul-cloner requires a bunch of ZUUL_* env variable which are provided
by Zuul scheduler when triggering a job.  Since the code coverage is
triggered by Jenkins own scheduler it is missing the ZUUL variable.

Thus hardcode required parameters in the job definition with sane
values.

Change-Id: I222afd038df073be9fd32796fd5d3bb564aeae9e