Use test_driver directly instead of CMake in the docker tests.
Deal with the read-only "/fish-source" by exporting
"CARGO_TARGET_DIR=$HOME/fish-build". It seems correct to also inject this
environment variable into the interactive debugging shells. Add some logging
to make this override more obvious to the user.
Adopt "build_tools/check.sh", because that defines the full set of checks
that we (eventually) want to run in CI.
In particular, this will also run "tests/checks/po-files-up-to-date.fish"
which "cargo b && cargo t && tests/test_driver.py" does not, due to the
REQUIRES clause.
Since most docker images have some lints/warnings today, disable those for
now. Use "docker_run_tests.sh --lint" to override. The default may be changed
in future.
The Dockerfiles had bitrotted some.
Get them passing again, add libpcre2-dev where we can so we aren't
hitting more servers than necessary, and reformat the bionic files so
they can share more of the same image.
