d/logger/journald: log journal-remote cmd output

Writing the systemd-journal-remote command output directly to os.Stdout
and os.Stderr makes it nearly impossible to tell which test case the
output is related to when the tests are not run in verbose mode. Extend
the journald sender fake to redirect output to the test log so they
interleave with the rest of the test output.

Signed-off-by: Cory Snider <csnider@mirantis.com>

daemon/logger/journald/internal/fake/sender.go

@@ -72,6 +72,10 @@ type Sender struct {
 	// https://github.com/systemd/systemd/commit/1eede158519e4e5ed22738c90cb57a91dbecb7f2
 	// (systemd 255).
 	BootID uuid.UUID
+
+	// When set, Send will act as a test helper and redirect
+	// systemd-journal-remote command output to the test log.
+	TB testing.TB
 }
 
 // New constructs a new Sender which will write journal entries to outpath. The
@@ -101,6 +105,7 @@ func NewT(t *testing.T, outpath string) *Sender {
 		t.Skip(err)
 	}
 	assert.NilError(t, err)
+	s.TB = t
 	return s
 }
 
@@ -109,6 +114,9 @@ var validVarName = regexp.MustCompile("^[A-Z0-9][A-Z0-9_]*$")
 // Send is a drop-in replacement for
 // github.com/coreos/go-systemd/v22/journal.Send.
 func (s *Sender) Send(message string, priority journal.Priority, vars map[string]string) error {
+	if s.TB != nil {
+		s.TB.Helper()
+	}
 	var buf bytes.Buffer
 	// https://systemd.io/JOURNAL_EXPORT_FORMATS/ says "if you are
 	// generating this format you shouldn’t care about these special
@@ -152,6 +160,16 @@ func (s *Sender) Send(message string, priority journal.Priority, vars map[string
 	// has been flushed to disk when Send returns.
 	cmd := exec.Command(s.CmdName, "--output", s.OutputPath, "-")
 	cmd.Stdin = &buf
+
+	if s.TB != nil {
+		out, err := cmd.CombinedOutput()
+		s.TB.Logf("[systemd-journal-remote] %s", out)
+		var exitErr *exec.ExitError
+		if errors.As(err, &exitErr) {
+			s.TB.Logf("systemd-journal-remote exit status: %d", exitErr.ExitCode())
+		}
+		return err
+	}
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr
 	return cmd.Run()