gomote, buildlet: add ls, push

Add gomote and buildlet support for listing remote files, and
efficiently syncing from the local workstation to the remote buildlet.

Change-Id: Ifab1fb1c208ca4bc66f8d6916c38e1914001a3a5
Reviewed-on: https://go-review.googlesource.com/4270
Reviewed-by: Andrew Gerrand <adg@golang.org>
9 files changed