Enabling multi-tenancy for fission objects. (#655)

This feature allows creation of fission objects in different namespaces, in addition to retaining the existing behavior of creating fission objects in default namespace if user doesnt provide one. 
It also removes cluster admin roles for fission-fetcher and fission-builder Service Accounts and grants them only those privileges that they need.

common.go

@@ -28,11 +28,15 @@ import (
 
 	"github.com/gorilla/handlers"
 	"github.com/imdario/mergo"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 	apiv1 "k8s.io/client-go/pkg/api/v1"
 )
 
-func UrlForFunction(name string) string {
+func UrlForFunction(name, namespace string) string {
 	prefix := "/fission-function"
+	if namespace != metav1.NamespaceDefault {
+		prefix = fmt.Sprintf("/fission-function/%s", namespace)
+	}
 	return fmt.Sprintf("%v/%v", prefix, name)
 }