Look for checkstyle-results everywhere, not just root dir

Tested by manually running mwext-cldr-phpcs-strict-HEAD which yields:

    Successfully parsed file
    mwext-cldr-phpcs-strict-HEAD/checkstyle-phpcs.xml

Updates jobs:

    apps-android-wikipedia-maven-checkstyle
    mediawiki-core-phpcs-HEAD
    mediawiki-core-phpcs-lenient
    mediawiki-core-phpcs-lenient-HEAD
    mediawiki-core-phpcs-strict
    mediawiki-core-phpcs-strict-HEAD
    mediawiki-core-regression-phpcs
    mediawiki-core-regression-phpcs-HEAD
    mwext-ContentTranslation-phpcs-strict-HEAD
    mwext-Interwiki-phpcs-strict-HEAD
    mwext-LocalisationUpdate-phpcs-strict-HEAD
    mwext-Translate-phpcs-strict
    mwext-Translate-phpcs-strict-HEAD
    mwext-TranslationNotifications-phpcs-strict-HEAD
    mwext-TwnMainPage-phpcs-strict-HEAD
    mwext-UniversalLanguageSelector-phpcs-strict-HEAD
    mwext-cldr-phpcs-strict-HEAD

Change-Id: I9f73accc996f411b6008f19d40c4412833c295d3