Added Bind method to Scheduler Extender

- only one extender can support the bind method
- if an extender supports bind, scheduler delegates the pod binding to the extender

plugin/pkg/scheduler/api/validation/validation_test.go

@@ -72,3 +72,15 @@ func TestValidateExtenderWithNegativeWeight(t *testing.T) {
 		t.Errorf("Expected error about priority weight for extender not being positive")
 	}
 }
+
+func TestValidateMultipleExtendersWithBind(t *testing.T) {
+	extenderPolicy := api.Policy{
+		ExtenderConfigs: []api.ExtenderConfig{
+			{URLPrefix: "http://127.0.0.1:8081/extender", BindVerb: "bind"},
+			{URLPrefix: "http://127.0.0.1:8082/extender", BindVerb: "bind"},
+		},
+	}
+	if ValidatePolicy(extenderPolicy) == nil {
+		t.Errorf("Expected failure when multiple extenders with bind")
+	}
+}