gs_archive_server: add list_dir rpc

The list_dir RPC lists all the files available inside a specific GS
archive URL. This RPC is necessary to implement fake omaha.

BUG=chromium:1078188
TEST=Ran curl -XGET
http://localhost:<gsa_port>/<image_archive>/<board>/<version>. Full
output can be found at http://gpaste/5738938083835904.

Change-Id: I6553b345bff6b84cb74e4466ce38d52dcea8bb10
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/dev-util/+/2274923
Tested-by: Sanika Kulkarni <sanikak@chromium.org>
Commit-Queue: Sanika Kulkarni <sanikak@chromium.org>
Reviewed-by: Congbin Guo <guocb@chromium.org>
Auto-Submit: Sanika Kulkarni <sanikak@chromium.org>
1 file changed