Run the wasm-jit library test in docker

[sjoelund]

The wasm-jit target needs the Rust omc, which the test nodes run too old an Ubuntu to build. Build it in the image the OpenModelica job uses, and run test.py there as well: an omc built against that image's glibc does not run on the node. Everything using the node's own omc (installing the libraries, the reference files, the database and publishing) stays outside.

runRegressiontest takes the directory of a Dockerfile; when given, the checkout+build script and the test.py script run through .inside() instead of sh. The testing repository is checked out before the omc build, since it provides that Dockerfile.

The image adds what the test tool needs on top of the build deps:

Added	Needed for
rsync, openssh-client	publishing the results
time, psmisc	time ./test.py, killall omc
venv from requirements	joblib, monotonic, natsort, psutil, ...
omc (stable)	--ompython_omhome, mos-file generation

The image's own venv only carries ompython and simplejson, and its apt sources point at the nightly component, so the sources list is switched to stable for a released reference omc.

Mounts: the node's home (the cached omc build, the libraries used as HOME during the run, the ssh key), /mnt/ReferenceFiles read-write since test.py caches a hash next to every reference file, /etc/passwd because ssh refuses to run for a uid it cannot look up, and the cargo registry volume of the OpenModelica job. --init reaps the omc processes test.py orphans.

sccache now starts inside the build script: a server started outside the container is of no use in it. Being the same image as the OpenModelica job also means its cache can hit at all, which it could not against a toolchain on the node, so the C parts get a compiler launcher too.