lib/deploy: Add structured logging info for syncfs() times

I plan to at some point change rpm-ostree to read the journal messages from
libostree and render things like the time we spent in syncfs().

Closes: #1044
Approved by: jlebon

src/libotutil/ot-log-utils.c

@@ -88,7 +88,7 @@ ot_log_structured (const char *message,
  *
  * Returns: %TRUE if stdout is (probably) connnected to the systemd journal
  */
-static gboolean
+gboolean
 ot_stdout_is_journal (void)
 {
   static gsize initialized;

src/libotutil/ot-log-utils.h

@@ -24,6 +24,8 @@
 
 G_BEGIN_DECLS
 
+gboolean ot_stdout_is_journal (void);
+
 void ot_log_structured_print_id_v (const char *message_id,
                                    const char *format,
                                    ...) G_GNUC_PRINTF(2, 3);