Improve process handling

[bt90]

The scrutiny container currently spawns multiple superfluous bash processes.

docker top scrutiny acxf yields:

PID                 TTY                 STAT                TIME                COMMAND
3265068             ?                   Ss                  0:00                \_ s6-svscan
3265188             ?                   S                   0:00                | \_ s6-supervise
3265397             ?                   S                   0:00                | \_ s6-supervise
3265402             ?                   Ss                  0:00                | | \_ bash
3265412             ?                   S                   0:00                | | \_ cron
3265398             ?                   S                   0:00                | \_ s6-supervise
3265406             ?                   Ss                  0:00                | | \_ bash
3265427             ?                   Sl                  1:10                | | \_ influxd
3265399             ?                   S                   0:00                | \_ s6-supervise
3265400             ?                   S                   0:00                | \_ s6-supervise
3265403             ?                   Ss                  0:00                | \_ bash
3265575             ?                   Sl                  0:03                | \_ scrutiny
3265821             pts/0               Ss+                 0:00                \_ sh

This PR switches the shell scripts to run their main process with exec effectively replacing the shells process.

[AnalogJ]

Interesting idea. Can you describe the use-case a bit? Is the intention to make monitoring cron within the container easier to do? Or is there some other reason you run docker top scrutiny acxf?

[bt90]

This is mostly about correct signal handling and a tiny bit to satisfy my OCD.

A bash proces - at least without traps - won't propagate signals to its child processes.

https://docs.docker.com/compose/faq/#why-do-my-services-take-10-seconds-to-recreate-or-stop

[AnalogJ]

seems reasonable. I'd appreciate if you confirm that the hub/spoke and omnibus images all work correctly after your changes, especially the cron and collector images.

[AnalogJ]

hey @bt90 have you had a chance to do any verification? I'd love to merge this PR

[bt90]

Sadly not yet. Not too much freetime ATM :(