devserver: Add functionality to stage artifacts from a local directory.

This change updates the devserver so that local build and
test artifacts  can be staged onto the devserver.

The devserver stage function will now also accept a local_path
as an argument. local_path specifies a subdirectory of the
devserver's static directory that contains build artifacts we
want to stage. It's restricted to a subdirectory of the static
directory in order to not allow callers access to the whole
file system of the devserver.

This functionality will be used in supporting custom image
staging for the new 'cros stage-on-moblab' command.

TEST=devserver_integration_test, unittests, & local moblab test run.
Change-Id: I617a61066e644657cdbfddee9762691c495d26b5
Reviewed-by: Simran Basi <>
Tested-by: Simran Basi <>
Commit-Queue: Simran Basi <>
5 files changed