Fix nginx reloading being broken in the config reloader.

This also fixes running the test suite. It turns out Nginx reloading had
been broken for a while, but 8d7ae67260902af093f327e9992cfac1d2644942
just broke the test suite due to changes in the order of the config file
writing (nginx now needs to be reloaded once during the startup process
to read in the initial config).
Pull in edge-case DNS resolver issue from gatekeeper codebase.

This got fixed for api.data.gov which is still using the older
gatekeeper and router where this DNS class resides there. But we need to
pull it in here for moving forward. See:
https://github.com/NREL/api-umbrella-gatekeeper/commit/bdb2be2146d60c670ccde98e477c9fc323ca9dfd
Fix moment deprecation for the subtract method.
Pull in the config reloader tests from the gatkeeper project.

These tests are far from ideal, and more work needs to be done here, but
it at least gets some of the DNS stuff testing again since the code
reorganization now that those classes live here.