Fix typo in client_source.rb that failed RHEL client installs

Array typo that resulted in debian packages being installed on RHEL systems.  Found via Test Kitchen run.  Introduced in COOK-3577
Minor readme typo

support -> supports
Add customization points for Icinga cookbook
Don't reuse resource names.
Use correct source for main config
Unify pagerduty script name
rubocop
Merge pull request #173 from mpasternacki/COOK-3287

[COOK-3287] Add customization points for Icinga cookbook
Update nagios plugins to the latest URL to fix broken RHEL NRPE and
nagios installs