lxd: tar and compress image in single stream

BUG=chromium:912638
TEST=local device
CQ-DEPEND=CL:1457259

Change-Id: Id6648ba21887c0b4cb274fc2e5d1271f40deaa8c
Reviewed-on: https://chromium-review.googlesource.com/1457957
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Joel Hockey <joelhockey@chromium.org>
Reviewed-by: Stephen Barber <smbarber@chromium.org>
3 files changed