Explicitly check if the data bag exists.

Rather than relying on failures from search we can retrieve the list
of databags and check if the data bag exists before searching.
Refactor data bag search into helper class
Whitespace cleanup.
Fix reference to undefined variable data_bags.
Don't create NRPE commands via the client recipe / remove attributes for these
Remove all non-NRPE commands / services except for check_nagios
Remove NRPE check tuneable attributes from Readme

Also cleanup a few items in the readme for clarity
Remove the nagios plugins that were copied in

This should now be handled by the user on a per check basis
Improvements to the Readme to help new users
Add nagios_services example data bags and an example recipe that uses the checknrpe LWRP
Merge remote-tracking branch 'opscode/ssd/search-refactor' into version-4-refactor
[COOK-2285] - fixes bugs in search helper

* best to pass in strings to the search
* require the query library, and use the search method rather than
  bare search (doesn't work in "libraries")
* pass a block to the search so the results come back as an array that
  can be iterated in the recipe
Ensure that the Nagios node is always added to all relevant host groups
Merge branch 'COOK-1554' into version-4-refactor
examples should use groups other than 'all'
Merge in cas authentication.
nrpe init script supports status
don't mention intervals twice when parsing data bags
Merge branch 'ben.v4' into jtimberman/v4
[COOK-2341] Corrected remote to pagerduty_nagios.pl