sync: dump git output on errors
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 <66788d848ab03efc83371cd4b586a3110f9172ef@google.com>
Tested-by: Mike Frysinger <8f3f75c74bd5184edcfa6534cab3c13a00a2f794@google.com>

lewixliu/git-repo,GerritCodeReview/git-repo,couchbasedeps/git-repo,couchbasedeps/git-repo,GerritCodeReview/git-repo,lewixliu/git-repo