Update to use newrelic-ng cookbook instead of newrelic

A better supported, better tested cookbook, using providers instead of
recipes. See https://github.com/chr4-cookbooks/newrelic-ng.
Clean up Vagrantfile to work w/ Vagrant 1.3+
Remove minitest-handler from Vagrantfile

No need to run tests during a simple Vagrant provision.
We'll use Test Kitchen for this instead.
Merge pull request #1 from evertrue/jeff/use-newrelic-ng

Switch to using newrelic-ng instead of newrelic cookbook