Fix jenkins rostam config

[G-071]

The available compiler and machine configuration on Rostam changed (breaking the rostam Jenkins pipeline).

This PR resolves any issues regarding this!

I further took the opportunity and streamlined the entire pipeline while I was at it:

• The tests are now being run on all available CUDA machines, speeding the testing up.
• The tests are now only triggered by the Jenkins branch indexing (queried every 5 minutes). This seems to work more reliably than the push trigger
• Removed ci_skip (it had the unfortunate tendency of skipping a test on a merge if just one out of X commits had the ci_skip annotation).
• Test logs are being stored for a longer duration.
• Reduced Jenkins Emails verbosity.

[diehlpk]

LGTM!