Fix several minor issues with Debian sysvinit script

- add `set -e` to make failing commands bail the script
- remove trailing `exit 0` which is just extraneous anyhow
- adjust `status_of_proc` options to pass in `$DOCKER_DESC` so we get consistently styled messages like `Docker is running` or `Docker is not running` or `could not access PID file for Docker`

Fixes #7424
Closes #7177