sync: dump git output on errors

Bug: https://crbug.com/gerrit/14700
Change-Id: I1ae53dc7f3792b7e8f11d73f706864fb6591eee8
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/311142
Reviewed-by: Raman Tenneti <rtenneti@google.com>
Tested-by: Mike Frysinger <vapier@google.com>
diff --git a/subcmds/sync.py b/subcmds/sync.py
index 8defc93..82eb569 100644
--- a/subcmds/sync.py
+++ b/subcmds/sync.py
@@ -360,7 +360,7 @@
           partial_clone_exclude=self.manifest.PartialCloneExclude)
 
       output = buf.getvalue()
-      if opt.verbose and output:
+      if (opt.verbose or not success) and output:
         print('\n' + output.rstrip())
 
       if not success: