pip_install_wheel: improved wheel filename guess

pip_install_wheel: improved wheel filename guess

Rather than only use PYPI_PACKAGE as a guess, fall back on PN for cases
where a recipe does not inherit pypi.

Wheels can only have alphanumeric characters in the 'distribution'
name [1]. Any other characters are replaced with an underscore. Provide a
function to replace dash with underscore.

[1] https://www.python.org/dev/peps/pep-0491/#escaping-and-unicode

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