Add the ability to install nrpe/plugins from packages on rhel/fedora

Installs from EPEL which adds yum as a requirement.  On Fedora >17 it
does not require epel.  There's a new attribute for packages since the
rhel packages break out every plugin into a package.
[COOK-2450] Add ability to define service groups through data bags.
[COOK-2308] Allow specifying hostgroups to not monitor/ignore.
Add missing library.
[COOK-2307] Added monitored_client_interface functionality.
Move attribute under server.
Should use n['ipaddress'] instead of node['ipaddress']
Move default['nagios']['server']['monitored_client_interface'] to attributes/server.rb
Add url for ohai network_addr plugin.
Update ohai network_addr plugin info.
Remove extraneous <%
Missing else clause.
Create a warning in the chef logs if a node doesn't have monitored_client_interface defined.
Fixed accidental reversion while rebasing.
Describe to new behavior in the README
Merge branch 'add_servicegroup_databags' of github.com:scottso/nagios into att-v4
Merge branch 'ignored_service_hostgroups' of github.com:scottso/nagios into att-v4
Merge branch 'monitored_client_interface' of github.com:scottso/nagios into att-v4

Conflicts:
	attributes/server.rb
Add hostname normalization to lowercase.
Add ability to have notes and notes_url entries for hosts.