Setup for PAM tests in buildbot

There are a few MTR tests which require PAM setup. In the old buildbot, they are run by a separate test step which is configured here
https://github.com/MariaDB/mariadb.org-tools/blob/d517f194308055c8fda5279dd6e1343758452388/buildbot/maria-master.cfg#L1426-L1556

It enables the minimal required configuration and runs the tests.

In the new buildbot they are currently skipped because there is no setup, they should be activated. It doesn't have to be done literally the same way as in the old buildbot, maybe it should be scripted better or configured more efficiently, as long as it works.