Fix bad variable '_' vs '::' naming issue

[jpknoll]

for some reason my installation isn't seeing the _ variable.

[alvagante]

Actually that's not a bad variable name, it's intended to be a top scope variable where you manage either where nagios files are ($::nagios_customconfigdir) or the criteria you can use to group different hosts under different nagios servers ($::nagios_grouplogic). This can't refer to the vars in params because they are used on the target nodes (where Nagios is actually not installed) and export resources to the Nagios server (which may have a different OS than the target nodes).

Documentation lacks important details and the solution works even if it's not perfect. Generally speaking:

• For $::nagios_customconfigdir Do nothing if your nagios configuration dir is /etc/nagios/ It it's somewhere else, for example in /etc/nagios3, set it to /etc/nagios3/auto.d
• For $::nagios_grouplogic Do nothing if you want only one Nagios server Set it to the name of the variable you want to use as discriminator, if you want to use different Nagios server. For example set it to 'env' if you want different Nagios servers for different environments (if you define your environment with the 'env' variable, that is).