Print the message asking the user to upload gerrit logs for git-cl upload
failures after the exception.

Also, initialize the error logger only for git-cl upload, so that the
headers are not overwritten unless git-cl upload is executed again.

Bug: 881860
Change-Id: I8e63432eecca5253e56096e3ad0218eec4058e12
Reviewed-on: https://chromium-review.googlesource.com/c/1277426
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>