Revise stash for BBOTAs when needed.

When generating incremental BBOTAs (v2 and above), we need to ensure
that the needed runtime stash is below the given threshold. If it's
running out of space on /cache, we replace the command that uses a
stash with a "new" command instead.

This may increase the OTA package size, since it is carrying more full
blocks instead of patches. It gets even worse for large files that span
a number of blocks, because currently we will store all the blocks for
the file as "new" blocks if stashing cannot be satisfied. We may further
optimize by splitting them into smaller chunks so that most of them can
still be stashed.

Bug: 22430577
Change-Id: Ieae5243d461e3f899f613f76a380f6f7c3edb356
(cherry picked from commit 82c47981)