Path to PHPUnit as deployed by Wikimedia deployment system.

The path is passed to MediaWiki php wrapper using --with-phpunitdir.  It
should match a local checkout of integration/phpunit.git repository
which contains PHPUnit as it is installed by Composer. The local copy
should be deployed on all slaves via the role::ci::slave puppet class
includes: deployment::target { # 'contint-production-slaves': }

Impacts the jobs:

mediawiki-core-phpunit-api
mediawiki-core-phpunit-databaseless
mediawiki-core-phpunit-misc
mediawiki-core-phpunit-parser
mediawiki-core-regression-REL1_19
mediawiki-core-regression-REL1_20
mediawiki-core-regression-REL1_21
mediawiki-core-regression-REL1_22
mediawiki-core-regression-master

Change-Id: I8651f2fb0e09d4e868c2139b5a7d1b640de61784