checkstyle publisher for phpcs

JSLint uses the checkstyle publisher whereas phpcs use the violations
one.  This change adds checkstyle processing to the phpcs jobs of
mediawiki core.  We will see how it looks like.

Updates jobs:
- mediawiki-core-phpcs-HEAD
- mediawiki-core-regression-phpcs
- mediawiki-core-regression-phpcs-HEAD
- test-mediawiki-phpcs-HEAD

Change-Id: I870405ee787d1be281f5f32b54519026e807260e