Disable stateful update install except for canaries.

This changes machine_install() to force a full update
(i.e. disallow install by stateful-only update) except for
canary/release builders.

BUG=chromium:360944
TEST=None

Change-Id: I4a6ebad6f926d01972f957c7ddcc6417864ac8f0
Reviewed-on: https://chromium-review.googlesource.com/193517
Reviewed-by: Dan Shi <dshi@chromium.org>
Commit-Queue: Richard Barnette <jrbarnette@chromium.org>
Tested-by: Richard Barnette <jrbarnette@chromium.org>
1 file changed