Make the error useful when Sensu hasn't been included.
Make the error useful when Sensu hasn't been included.

This transforms the error message from something like:
Unknown variable: '::sensu::check_notify'. at /etc/puppet/environments/masterbranch/vendor/modules/sensu/manifests/check.pp:147:28
into the much more helpful:
Error while evaluating a Function Call, monitoring_check local_smtp defined before the sensu class was included at /etc/puppet/environments/masterbranch/vendor/modules/monitoring_check/manifests/init.pp:266:7

Yelp/puppet-monitoring_check,Yelp/puppet-monitoring_check,somic/puppet-monitoring_check,jglukasik/puppet-monitoring_check,jglukasik/puppet-monitoring_check,somic/puppet-monitoring_check