cluster: introduce RegionIterator

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

pkg/cluster/regions.go

@@ -8,8 +8,15 @@ import (
 var (
 	_ MachineIterator = (*Region)(nil)
 	_ ZoneIterator    = (*Region)(nil)
+
+	_ RegionIterator = (*Cluster)(nil)
 )
 
+// A RegionIterator is a set of Regions we can iterate on
+type RegionIterator interface {
+	ForEachRegion(func(*Region) bool)
+}
+
 // Region represents a group of zones geographically related
 type Region struct {
 	m     *Cluster