MDLSITE-2094: Look for some more strings on phpunit output

Link: https://tracker.moodle.org/browse/MDLSITE-2094

We were already looking for some PHP stack traces to detect any problem when running unit tests. But that was not enough to get debugging and/or other stack traces.

So the patch introduces two more searches within the output of phpunit tests to detect any "Debugging:" output and also any general backtrace information ("line XX of XXXX: call to").

Seems to be working here. Ciao :-)