Trailing server.pid

[mika018]

Sometimes rails leaves a trailing /usr/src/app/tmp/pids/server.pid file in the container causing it not to be able to restart.
We fixed the latest incident reported here https://github.com/epimorphics/hmlr-ansible-deployment/issues/72 by removing the file manually but it would be nice if we can know exactly how it is left behind.

A potential solution is to just add

rm -f /usr/src/app/tmp/pids/server.pid

at the start of the entrypoint.sh script but not sure if that is the right solution. It is treating the consequence rather than the cause.