nagios: Use canonical "hostgroup_name" consistently.
nagios: Use canonical "hostgroup_name" consistently.

zulip/zulip,zulip/zulip,zulip/zulip,rht/zulip,rht/zulip,zulip/zulip,andersk/zulip,rht/zulip,andersk/zulip,andersk/zulip,rht/zulip,andersk/zulip,zulip/zulip,andersk/zulip,zulip/zulip,rht/zulip,rht/zulip,andersk/zulip,rht/zulip,zulip/zulip,andersk/zulip