cluster: introduce Machine.Inactive flag

if a Machine is Inactive, it won't be included on the DNS
aliases for the zone or it's regions.

Signed-off-by: Alejandro Mery <amery@jpi.io>

pkg/cluster/regions.go

@@ -32,7 +32,9 @@ func (r *Region) ForEachMachine(fn func(*Machine) bool) {
 		var term bool
 
 		z.ForEachMachine(func(p *Machine) bool {
-			term = fn(p)
+			if p.Active() {
+				term = fn(p)
+			}
 			return term
 		})