Extend the API in order to be able to write out the file checksum cache
onto disk. SignatureGeneratorBasic class now implements a method that
update the fetcher local files checksum cache with the task file
dependency checksums.
(Bitbake rev: ecdabd321d48fa367b89ebffc00aa525b6eaa95c)
Signed-off-by: Markus Lehtonen <markus.lehtonen@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>