Add config options to enable fine grained control of what's tested in a PR

Currently we have a fixed set of Jenkins CI config profiles when testing PRs (QA_JTS_JDKORB, QA_JTA, XTS, MAIN, BLACKTIE and PERF) and we are allowed to selectively disable one or more of them.

It would be handy to be able to control other things such as running QA tests using the journal store (which none of the above QA profiles allow). It would also be a handy shortcut to explicitly set which profile to run (as opposed to which ones to disable).