Sensu Plugins Azure ACR Quota Metrics

This is a hacky Sensu plug-in to call out to the az to list all ACRs (Azure Container Registries) in a subscription and get quota usage metrics.

Note: Quota metrics are only available for 'managed' ACRs, and so the Classic sku is ignored.

The gem assumes virualenv, python and pip are installed, and will run install.bash as a pre-gem hook to install a virualenv and the required az command. Ick.

Tested on Ruby 2.3.

The unit test is a bit dubious, and it's almost impossible to run unit tests on Sensu plug-ins as they run as soon as scoped... The test must be run from the root directory also.

bundle exec rspec should run the test, after bundle installing of course.

Why call out to az instead of using the Ruby SDK?

There's very little documentation and this was the path of least resistance.

I'm open to re-writes which use the Ruby Gems instead. You'll need the azure_mgmt_compute and azure_mgmt_monitor gems.