Better kubelet logging for probes

Log when we actually run probes and event when they fail.  Print the output of
a probe, too.

pkg/probe/tcp/tcp_test.go

@@ -22,6 +22,7 @@ import (
 	"net/http/httptest"
 	"net/url"
 	"strconv"
+	"strings"
 	"testing"
 	"time"
 
@@ -34,10 +35,11 @@ func TestTcpHealthChecker(t *testing.T) {
 		expectedStatus probe.Result
 		usePort        bool
 		expectError    bool
+		output         string
 	}{
 		// The probe will be filled in below.  This is primarily testing that a connection is made.
-		{probe.Success, true, false},
-		{probe.Failure, false, false},
+		{probe.Success, true, false, ""},
+		{probe.Failure, false, false, "tcp: unknown port"},
 	}
 
 	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
@@ -60,7 +62,7 @@ func TestTcpHealthChecker(t *testing.T) {
 		if !test.usePort {
 			p = -1
 		}
-		status, err := prober.Probe(host, p, 1*time.Second)
+		status, output, err := prober.Probe(host, p, 1*time.Second)
 		if status != test.expectedStatus {
 			t.Errorf("expected: %v, got: %v", test.expectedStatus, status)
 		}
@@ -70,5 +72,8 @@ func TestTcpHealthChecker(t *testing.T) {
 		if err == nil && test.expectError {
 			t.Errorf("unexpected non-error.")
 		}
+		if !strings.Contains(output, test.output) {
+			t.Errorf("expected %s, got %s", test.output, output)
+		}
 	}
 }