New utility for creating bootcache.

The bootcache utility access information exported by
dm-bootcache device mapper to create a boot cache
store.

BUG=chromium-os:25441
TEST=wrote a test program to exercise code.

Change-Id: I729926f5fbc125a543084647f6cc87b8ab214745
Reviewed-on: https://gerrit.chromium.org/gerrit/27703
Tested-by: Paul Taysom <taysom@chromium.org>
Reviewed-by: Luigi Semenzato <semenzato@chromium.org>
Commit-Ready: Paul Taysom <taysom@chromium.org>
5 files changed