Jörg Werner

The first part was solved with #295.

Looks like `ThreadLocalRandom` cannot be reseeded which is needed for our "replayable randomness" feature.

Building the XLT docker image can be done with `packer`. See https://github.com/Xceptance/XLT-Packer/issues/5 for more info.

Labeling rules are similar to merge rules, so applied the same mechanism here. Also reused the rule configuration syntax.