recipetool; add support for python_mesonpy class

recipetool; add support for python_mesonpy class

* Add support to detect the "mesonpy" build-backend for recipetool create.
* Add oe-selftest case for creating a recipe for "siphash24" from pypi.
  https://pypi.org/project/siphash24/

This is by far the simplest recipe using the mesonpy build backend.

Upstream does not provide LICENSE file(s) and we do not detect the
LICENSE so don't check for that result in the test. Likewise, upstream
does not define HOMEPAGE, so skip that result.

Signed-off-by: Tim Orling <tim.orling@konsulko.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>