[TASK] Simplify PHP lint execution

This simplifies PHP lint execution in Travis by ensuring lint
errors are outputted to stderr and drops everything else. If
any check fails, the exit code 1 is returned.

The Composer vendor directory is excluded from linting.

Resolves: #66437
Releases: master
Change-Id: I588a880f548c248a0db44f3a3f1274fcec2edd00
Reviewed-on: http://review.typo3.org/38704


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>