Skip long light 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 from about 21s to about 0.9s.

light/detector_test.go

@@ -235,6 +235,10 @@ func TestLightClientAttackEvidence_Equivocation(t *testing.T) {
 }
 
 func TestLightClientAttackEvidence_ForwardLunatic(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+
 	// primary performs a lunatic attack but changes the time of the header to
 	// something in the future relative to the blockchain
 	var (

light/example_test.go

@@ -17,6 +17,10 @@ import (
 
 // Manually getting light blocks and verifying them.
 func TestExampleClient(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 	conf, err := rpctest.CreateConfig(t, "ExampleClient_VerifyLightBlockAtHeight")

light/light_test.go

@@ -23,6 +23,10 @@ import (
 
 // Automatically getting new headers and verifying them.
 func TestClientIntegration_Update(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+
 	t.Parallel()
 
 	ctx, cancel := context.WithCancel(context.Background())
@@ -84,6 +88,10 @@ func TestClientIntegration_Update(t *testing.T) {
 
 // Manually getting light blocks and verifying them.
 func TestClientIntegration_VerifyLightBlockAtHeight(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+
 	t.Parallel()
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
@@ -162,6 +170,10 @@ func waitForBlock(ctx context.Context, p provider.Provider, height int64) (*type
 }
 
 func TestClientStatusRPC(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping test in short mode")
+	}
+
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
 	conf, err := rpctest.CreateConfig(t, t.Name())