lntest: make it clear that profile failure is follow-up error

From the error in the itest output log it is not clear whether scraping
the profile page caused a test to fail or whether it was just a
follow-up error. We make it a bit more clear with an added message.

lntest/harness.go

@@ -840,7 +840,7 @@ func (n *NetworkHarness) StopNode(node *HarnessNode) error {
 
 // SaveProfilesPages hits profiles pages of all active nodes and writes it to
 // disk using a similar naming scheme as to the regular set of logs.
-func (n *NetworkHarness) SaveProfilesPages() {
+func (n *NetworkHarness) SaveProfilesPages(t *testing.T) {
 	// Only write gorutine dumps if flag is active.
 	if !(*goroutineDump) {
 		return
@@ -848,7 +848,8 @@ func (n *NetworkHarness) SaveProfilesPages() {
 
 	for _, node := range n.activeNodes {
 		if err := saveProfilesPage(node); err != nil {
-			fmt.Printf("Error: %v\n", err)
+			t.Logf("Logging follow-up error only, see rest of "+
+				"the log for actual cause: %v\n", err)
 		}
 	}
 }

lntest/itest/test_harness.go

@@ -82,7 +82,7 @@ func (h *harnessTest) Skipf(format string, args ...interface{}) {
 // the error stack traces it produces.
 func (h *harnessTest) Fatalf(format string, a ...interface{}) {
 	if h.lndHarness != nil {
-		h.lndHarness.SaveProfilesPages()
+		h.lndHarness.SaveProfilesPages(h.t)
 	}
 
 	stacktrace := errors.Wrap(fmt.Sprintf(format, a...), 1).ErrorStack()

lntest/node.go

@@ -1167,7 +1167,8 @@ func (hn *HarnessNode) stop() error {
 	if hn.conn != nil {
 		err := hn.conn.Close()
 		if err != nil {
-			return fmt.Errorf("error attempting to stop grpc client: %v", err)
+			return fmt.Errorf("error attempting to stop grpc "+
+				"client: %v", err)
 		}
 	}