Add support for configuring Nagios Event Brokers

Merged my changes for managing Nagios Event Brokers into the current upstream cookbook release.

These changes allow another cookbook to do the following to pass the configuration of a nagios event broker to the nagios cookbook for inclusion in the config.

node.set['nagios']['brokers']['/path/to/broker.o'] = 'config_foo=1,config_bar=spork'