Remove global app references (#7433)

* remove global app references

* test fix

* fix api4 test compilation

app/cluster_discovery_test.go

@@ -12,8 +12,7 @@ import (
 )
 
 func TestClusterDiscoveryService(t *testing.T) {
-	a := Global()
-	a.Setup()
+	Setup()
 
 	ds := NewClusterDiscoveryService()
 	ds.Type = model.CDS_TYPE_APP