Assign all hosts to a nagios hostgroup

monitor_host does not assign 'misc' cluster hosts to any group. This
behaviour is very well documented in both in comments in source and in
I50c8d5c96b2541b1b926a98c8006ccdc665665e6
Undo this behaviour and assign all hosts, including misc ones to a
cluster.

Change-Id: Ia6207bd51b53784f78f51230f0ae74f64cf74504
Merge "Assign all hosts to a nagios hostgroup" into production