pass blobs to applypatch in incremental OTAs

applypatch now takes patches as blob-valued arguments instead of just
filenames, eliminating the need to unpack all patches to /tmp before
starting to apply them.

Revert the last change I made where sha1_check(read_file(...)) was
substituted for apply_patch_check(...).  apply_patch_check() knows to
check /cache/saved.file if the original source file is missing or has
a bad checksum, which is important if the device loses power or
otherwise restarts during patching.

Change-Id: Ia5b761474b0f809a5a5eed29455b1b145145699e