Skip long rpc/jsonrpc 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 rpc/jsonrpc from about 8.3s to about 2.3s.

rpc/jsonrpc/jsonrpc_test.go

@@ -340,6 +340,10 @@ func TestRPC(t *testing.T) {
 		}
 	})
 	t.Run("WSClientPingPong", func(t *testing.T) {
+		if testing.Short() {
+			t.Skip("skipping test in short mode")
+		}
+
 		// TestWSClientPingPong checks that a client & server exchange pings
 		// & pongs so connection stays alive.
 		t.Cleanup(leaktest.CheckTimeout(t, 4*time.Second))