Add Nagios Core config management

[jomann09]

On designated systems, automatically update Nagios Core configuration with changes when they are applied. Systems are designated as having Nagios Core installed from the Manager.

When agent is set to use the manager:

• Add Nagios Core config check to sync
• Have rcagent check for Nagios Core in normal locations (/opt, /usr/local)
• Download and apply Nagios Core configs on change (via restart if configured from manager to do so)