Fix incorrect server packages

Nagios failed to install on Debian/Ubuntu.  Nagios should be Nagios3.  Found and confirmed via Test Kitchen
Clarify the new attribute for server and vname for icinga installs
Merge pull request #200 from tas50/master

[COOK-3729] - Update nagios plugins to the latest URL to fix broken RHEL NRPE installs
Drop TK memory allocation for clients from 1024 -> 512

Tested that this is still enough to compile the NRPE client.  No need to allocate more than that since some people only have dev systems with 4GB ram.