fix: ensure jm working dir exists

[theborakompanioni]

Fix for missing jm working directory if it is not mapped to the host system.

The log feature introduced a regression bug, when the logs moved from directory $JM_WORK_DIR/logs to /var/log/jam.
Since then, it was not ensured that the directory actually exists.

In most setups this is no problem, as the directory will most probably always be mapped to the host system via --volume jmdatadir:/root/.joinmarket, but in some situation, e.g. just starting the image once, this might lead to an error when the config file is copied: cp: cannot create regular file '/root/.joinmarket/joinmarket.cfg': No such file or directory.

The added line mkdir --parents "${DATADIR}/" now creates the directory in case it is missing.

Small additional change: In order to prevent supervisord from searching for its configuration file in multiple locations and printing a warning message to stdout, the path to the config file is passed as a parameter.

[theborakompanioni]

Not totally sure if this is the right approach, to be honest. Maybe instead of creating the dir, we should exit with a more descriptive error indicating that the directory should be mapped to the host system? Let me know what you think @dergigi

[dergigi]

I think creating the directory is fine. There shouldn't be any bad side-effects to this, and personally I prefer fixing things that can be fixed easily as opposed to throwing errors for things that the user should not have to care about.

[dergigi]

Looks good to me, feel free to merge ✅