We use `timeout` from the coreutils package (should be part of many basic
installations - maybe with a different name) to force the individual
healthcheck commands too exit after a predefined timeout (300s); if this
doesn't help, send a SIGKILL.

This should help with the initial problem of hanging. A next step should
be to catch the `timeout` invoked exit and log this as an exceptional
happening.

Address #60