recipetool: create_buildsys_python: add pypi support

recipetool: create_buildsys_python: add pypi support

Today, we can use devtool/recipetool to create recipes for python projects
using the github url or the direct release tarball of the project, but the
create_buildsys_python plugin doesn't support the pypi class, since we cannot
know from the extracted source if the package is available on pypi or not.

By implementing the new optional process_url callback, we can detect
that the url is a pypi one (i.e 'https://pypi.org/project/<package>')
and retrieve the release tarball location.
Also detect if the url points to a release tarball hosted on
"files.pythonhosted.iorg" (i.e https://files.pythonhosted.org/packages/...)

In both cases, adds the pypi class, remove 'S' and 'SRC_URIxxx'
variables from the created recipe as they will be handled by the pypi class
and add the PYPI_PACKAGE variable

This helps to produce cleaner recipes when package is hosted on pypi.

If the url points to a github url or a release tarball not coming from
"files.pythonhosted.org", the created recipe is the same as before.
One can also use the newly added "--no-pypi" switch to NOT inherit
from pypi class on matching url, to keep legacy behaviour.

To create a recipe for a pypi package, one can now use one of the
new following syntax (using recipetool create / devtool add):

* recipetool create https://pypi.org/project/<package>
* recipetool create https://pypi.org/project/<package>/<version>
* recipetool create https://pypi.org/project/<package> --version <version>

or the old syntax:
* recipetool create https://files.pythonhosted.org/packages/<...>

Signed-off-by: Julien Stephan <jstephan@baylibre.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>