every environment is defined as nagios hostsgroup (#5216)

Change-Id: I6508ce0d06b37a1c5601a0e981a59f7fda47f76a
include different nagios::defaults classes manually (#5216)

nagios::defaults will include nagios::defaults::hostgroups which
add "all" and "centos_servers" hostgroups which we don't want.

Change-Id: If42faa11c167fb7305ebbb21dc358a8813afaa25
Merge branch '5216_nagios_hostgroups' into develop