[TASK] Find functional tests automatically, optimize travis-ci

Simalar to UnitTests.xml, FunctionalTests.xml no longer register
single test suites but find all functional tests cases using a
wildcard.

For travis-ci, single tests cases are now given to parallel using
gnu find. This leads to a nice performance improvement on travis
since more but shorter processes are executed, sharing the available
hardware more effectively.

Change-Id: I8dc34ed2fcc1ae8390bc05dbe6f5e7009af17a36
Resolves: #58578
Related: #58533
Releases: 6.2
Reviewed-on: https://review.typo3.org/29901
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn