Resource manager: add service lister and remove unused lock. (#559)

* Remove unused lock from the resource manager.

* Add service lister to the resource manager.

This change adds a service lister in the
resource manager.
This will be used to set the service env vars.
Also added a List method to the resource manager
and a simple test to confirm it's a pass through.

providers/azure/aci_test.go

@@ -832,7 +832,7 @@ func createTestProvider(aadServerMocker *AADMock, aciServerMocker*ACIMock) (*ACI
 	os.Setenv("ACI_RESOURCE_GROUP", fakeResourceGroup)
 	os.Setenv("ACI_REGION", fakeRegion)
 
-	rm, err := manager.NewResourceManager(nil, nil, nil)
+	rm, err := manager.NewResourceManager(nil, nil, nil, nil)
 
 	if err != nil {
 		return nil, err