ktest: Sync before reboot

Before rebooting the target, run the sync command, as it seems that
either Grub2 or systemd gets screwed up if you update to reboot a kernel
once and do a reboot without doing a sync.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/tools/testing/ktest/ktest.pl b/tools/testing/ktest/ktest.pl
index 63245a5..f4b8f96 100755
--- a/tools/testing/ktest/ktest.pl
+++ b/tools/testing/ktest/ktest.pl
@@ -1147,6 +1147,9 @@
 sub reboot {
     my ($time) = @_;
 
+    # Make sure everything has been written to disk
+    run_ssh("sync");
+
     if (defined($time)) {
 	start_monitor;
 	# flush out current monitor