devserver: Make quick provision handle /dev/sdaX partitions.

BUG=chromium:785083
TEST=build=auron_paine-paladin/R64-10083.0.0-rc2; curl "http://${ds}/stage?archive_url=gs://chromeos-image-archive/${build}&artifacts=quick_provision,stateful"; curl "http://${ds}/cros_au?full_update=False&force_update=True&build_name=${build}&host_name=${dut}&async=False&clobber_stateful=True&quick_provision=True"

Change-Id: If3336413a9b13dad427f33dc538df0a097cd0221
Reviewed-on: https://chromium-review.googlesource.com/772833
Commit-Ready: David Riley <davidriley@chromium.org>
Tested-by: David Riley <davidriley@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
1 file changed