Travis optimizations

 - disabled GC on running unit tests and cs fixer
 - allow to run more parallel processes than CPUs
 - ignore special folders ('_files' and 'AllTests') to run with phpunit
 - no longer keep order of parallel processes
  - this one isn't for all over performance but for humans - If you wait for a specific test case you will be informed asap the component has been ready

This should be make little performance improvements.

A much better performance improvement would be to run all unit tests and cs fixer in parallel, too.
But I currently haven't a good idea how to do that simplified.
@Ocramius What do you mean? The only PHP runtme difference is `zend.enable_gc=0` and it will be ignored by HHVM.