Make debian init work when called quickly.

We use the start-stop-daemon pid creation mechanism in addition the intrinsic built into docker.  This means the pid file is guaranteed to be written out by the time the script exits.

See #6184.

Docker-DCO-1.1-Signed-off-by: Joe Beda <joe.github@bedafamily.com> (github: jbeda)
Merge pull request #6185 from jbeda/debian-init-fix

Make debian init work when called repeatedly in quick succession