python: add mypy to pipenv

python: add mypy to pipenv

0.730 appears to be about the oldest version that works with the
features we want, including nice human readable output (to make sure
iotest 297 passes), and type-parameterized Popen generics.

0.770, however, supports adding 'strict' to the config file, so require
at least 0.770.

Now that we are checking a namespace package, we need to tell mypy to
allow PEP420 namespaces, so modify the mypy config as part of the move.

mypy can now be run from the python root by typing 'mypy -p qemu'.

A note on mypy invocation: Running it as "mypy qemu/" changes the import
path detection mechanisms in mypy slightly, and it will fail. See
https://github.com/python/mypy/issues/8584 for a decent entry point with
more breadcrumbs on the various behaviors that contribute to this subtle
difference.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Tested-by: Cleber Rosa <crosa@redhat.com>
Message-id: 20210527211715.394144-23-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>