make test-php-style

[mmattel]

For harmonisation, it would be good to have a make test-php-style as we have eg in core.
Please see also documentation: https://github.com/owncloud/documentation/issues/4064#issuecomment-412053981 plus follow up comment

This would:

• ease up development
• have a documentation that matches different repo setups

@phil-davis @DeepDiver1975

Part of owncloud/QA#582

[ownclouders]

GitMate.io thinks possibly related issues are #55 (php-cs-fixer), #28 (Test against master again), #13 (Test with php 5.6 up to 7.2 - ensure composer compatibility with php 5.6), #49 (Add unit tests), and #86 (Add litmus to testing pipeline).

[phil-davis]

I an currently looking to create a standard set of CI-drone-Makefile-test scripts in each app repo. So this will happen naturally as I do that.