Bug 60694: Make the config file path configurable

This is a stop-gap solution to get bug 60694 fixed by supporting a different
config file path in beta vs. production.

In the longer term we should probably puppetize /etc/parsoid/settings.js
differently, and use the Debian package as developed in
https://gerrit.wikimedia.org/r/#/c/110666/ for installs.

Change-Id: I51b26c0aed75f8a8614c560c45b98320b74c31e0
Merge "Bug 60694: Make the config file path configurable" into production