gs_archive_server: download content when request is not HEAD

StreamingCat method is called in download RPC even when the request is a
HEAD request. Add a check to see if the request is HEAD or GET and call
StreamingCat only when it is GET.

BUG=chromium:1077020
TEST=Tested on chromeos2-devservertest using steps in description on the
bug

Change-Id: I51bade777db70bb7b085e250b67374c82122baf8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2200073
Tested-by: Sanika Kulkarni <sanikak@chromium.org>
Commit-Queue: Sanika Kulkarni <sanikak@chromium.org>
Auto-Submit: Sanika Kulkarni <sanikak@chromium.org>
Reviewed-by: Congbin Guo <guocb@chromium.org>
1 file changed