add SupportDatastoreEmulator field to aetest Options (#173)

Pass through --support_datastore_emulator. https://issuetracker.google.com/issues/119212211

aetest/instance.go

@@ -25,6 +25,9 @@ type Options struct {
 	// StronglyConsistentDatastore is whether the local datastore should be
 	// strongly consistent. This will diverge from production behaviour.
 	StronglyConsistentDatastore bool
+	// SupportDatastoreEmulator is whether use Cloud Datastore Emulator or
+	// use old SQLite based Datastore backend or use default settings.
+	SupportDatastoreEmulator *bool
 	// SuppressDevAppServerLog is whether the dev_appserver running in tests
 	// should output logs.
 	SuppressDevAppServerLog bool

aetest/instance_vm.go

@@ -201,6 +201,9 @@ func (i *instance) startChild() (err error) {
 	if i.opts != nil && i.opts.StronglyConsistentDatastore {
 		appserverArgs = append(appserverArgs, "--datastore_consistency_policy=consistent")
 	}
+	if i.opts != nil && i.opts.SupportDatastoreEmulator != nil {
+		appserverArgs = append(appserverArgs, fmt.Sprintf("--support_datastore_emulator=%t", *i.opts.SupportDatastoreEmulator))
+	}
 	appserverArgs = append(appserverArgs, filepath.Join(i.appDir, "app"))
 
 	i.child = exec.Command(python,