python: add optional FUSE dependencies

python: add optional FUSE dependencies

In preparation for moving qom-fuse over to the python package, we need
some new dependencies to support it.

Add an optional 'fusepy' dependency that users of the package can opt
into with e.g. "pip install qemu[fuse]" which installs the requirements
necessary to obtain the additional functionality.

Add the same fusepy dependency to the 'devel' extras group --
unfortunately I do not see a way for optional groups to imply other
optional groups at present, so the dependency is repeated. The
development group needs to include the full set of dependencies for the
purpose of static analysis of all features offered by this library.

Lastly, add the [fuse] extras group to tox's configuration as a
workaround so that if a stale tox environment is found when running
`make check-tox`, tox will know to rebuild its environments.

Signed-off-by: John Snow <jsnow@redhat.com>
Message-id: 20210603003719.1321369-17-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>