Fix HUP kill not reloading config

[acalcutt]

This is a fix for #629, which was broken in the syntax change of #606

After looking at the code changes, it seems like the sections of code that handles SIGINT/SIGHUP and restarting was not being used anymore. This change renames the functions a bit so the SIGINT/SIGHUP code is actually used.

[zstadler]

I have tested this PR under Docker and it fixes #629: reloading of an updated config file works in both ways:

• The documented preferred way: docker kill -s HUP tileserver-gl
• The older way: docker exec tileserver-gl bash -c 'kill -HUP $(ls -l /proc/*/exe | sed -n "/\/node$/s/.*proc\/\([0-9]\+\)\/exe .*/\1/p")

[mnutt]

I suspect that clearing the require cache might have been to give the ability to reload options.dataDecorator which is loaded via require(). IMO that seems like it's approaching ad-hoc hot-reloading territory and I think it's fine to not support.

[zstadler]

Please consider resolving #629

[acalcutt]

I'm planning to resolve it after the docker is updated