Add hostname tagged metric
Add hostname tagged metric

This potentially allow prometheus smarter mapping like having:
sum by (host) (felix_active_local_endpoints * on (job, instance) group_left(host) felix_host)
instead of:
sum by (instance) (felix_active_local_endpoints)

neiljerram/felix,neiljerram/felix,Metaswitch/calico,neiljerram/felix,neiljerram/felix,Metaswitch/calico