bitbake: tinfoil: create simple interface for bitbake-based utilities

bitbake: tinfoil: create simple interface for bitbake-based utilities

The code to initialise BitBake within bitbake-layers should be useful
for other utilities that need to query configuration or recipe
information, so refactor it out into its own class, "Tinfoil" (to
continue with our cooking metaphor).

(Bitbake rev: e5707e3938ace47c4a8d1fa2e81583fd4dc6b95d)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>