SL-49406: template_verifier.py requires network access to build. Implemented...

SL-49406: template_verifier.py requires network access to build.  Implemented a 4-hour cache so it hits the network less often overall (saving approx .5 seconds every build), and added fault tolerance for when it fails to fetch the master over the network.  It'll whine at you if it can't fetch it, but even if it can't get the master from the network and doesn't have a cached copy at all, it will still at least do a syntax check on the local template.