The chain of executions is as is:
- `docker_build_and_run_tests_all.sh`
- launches several instances of `docker_build_and_run_tests.sh`
- builds docker images with the `target_role.sh` and `tester_role.sh` entrypoints
- inside the tester docker, `tester_role.sh` launches `launch_tests_on_instance.sh`
- the target docker gets tested after setting up accounts, SSH etc.
Previously, these scripts passed options to each other either by a mix of environment
variables and command-line arguments, with some inconsistencies here and there.
Now, `launch_tests_on_instance.sh` supports a lot of command-line options, which can
be specified directly if testing a remote server, or can be passed-through by the calling
script in case of docker tests. `docker_build_and_run_tests.sh` and
`docker_build_and_run_tests_all.sh` also support to passthrough these options down.
