SiteHost.verify_software checks space in the encrypted stateful partition

BUG=chromium-os:219686
TEST=Test with a lumpy device in both cases where the space
requirement was met and was not.

Change-Id: I1a319ac334629cdf6655ea9402ea0851fcd7a8a0
Reviewed-on: https://gerrit.chromium.org/gerrit/46037
Reviewed-by: Richard Barnette <jrbarnette@chromium.org>
Tested-by: Fang Deng <fdeng@chromium.org>
Commit-Queue: Fang Deng <fdeng@chromium.org>
3 files changed