Use common httpserver across fission (#2409)

* Defining httpserver package to capture httpserver shutdown and
introduces uniform running of http server across codebase.
* Add unit tests for httpserver

Signed-off-by: Sanket Sudake <sanketsudake@gmail.com>

pkg/storagesvc/client/storagesvc_test.go

@@ -209,7 +209,7 @@ func TestLocalStorageService(t *testing.T) {
 	storage := storagesvc.NewLocalStorage(localPath)
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
-	os.Setenv("METRICS_ADDR", ":8083")
+	os.Setenv("METRICS_ADDR", "8083")
 	_ = storagesvc.Start(ctx, logger, storage, port, true)
 
 	time.Sleep(time.Second)