Skip long light/provider/http tests in -short mode

I added checks against testing.Short for tests that took longer than
about one second on my machine. Running with -short reduces the test
time of light/provider/http from about 20s to about 0.3s.

light/provider/http/http_test.go

@@ -33,6 +33,10 @@ func TestNewProvider(t *testing.T) {
 }
 
 func TestProvider(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 	cfg, err := rpctest.CreateConfig(t, t.Name())