Adapt number of credentials tests executed based on system performance

Faster systems can run more tests in the same amount of time, so allow them
to run more tests, while the slower systems run fewer tests. Should increase
the chances that each authentication test is run at least once in the 
multi-configuration job.
Revert "Adapt number of credentials tests executed based on system performance"

This reverts commit 14bc4f381a2299aa7052a4d396185c5d8ab4b87b because
there is not enough benefit from the added complexity compared to
the tests which existed before.
Merge remote-tracking branch 'upstream/master' into master-fix-javadoc-for-java-8