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.
Describe to new behavior in the README
Merge pull request #134 from tas50/COOK-1068

Cook 1068: Allow the installation of NRPE using EPEL packages on RHEL / Fedora
Correct the IP check logic to check the right node

I had it checking the Nagios server's attributes before when I wanted
the search discovered node
Don't fail to write out services in the hostgroups databags

Fix the logic for checking for valid host groups
[COOK-2565] Update nginx.conf.erb for correct use AUTH
Merge pull request #140 from tas50/COOK-2257

COOK-2257: Correct the IP check logic to check the right node
[COOK-2474] don't assume node has cloud attributes

Prior to this the cookbook assumed if the server node had a cloud
attributes, every node had the cloud attributes, this removes this
assumption.
Merge branch 'COOK-2474'
Merge pull request #141 from tas50/COOK-2558

COOK-2558: Don't fail to write out services in the hostgroups databags
Merge pull request #139 from scottso/fix_config_perms

[COOK-2546] nrpe config files should not be world readable
Merge pull request #143 from pioneerit/COOK-2565

[COOK-2565] Update nginx.conf.erb for correct use AUTH
[COOK-2546] - use nagios user/group attribute
Removed extra "!("
Fix syntax if nagios_hostgroups data bag based search returns nothing

Don't write out "members empty" if nothing comes back from the search.
Instead write out a host group with nothing, which is actually correct.
 Also remove an empty line so that there is a single empty line between
each host group definition.
Merge pull request #144 from behrendsj/cook-2558

Removed extra "!("
Merge pull request #138 from scottso/normalize_hostnames

[COOK-2543] Add hostname normalization to lowercase.
Merge pull request #130 from scottso/add_servicegroup_databags

[COOK-2450] Add ability to define service groups through data bags.
Fix missing all wildcard. Fix intersect with node.run_list.roles instead of node.roles.
Merge branch 'COOK-2541'