Introduce a Python module structure

Introduce a Python module structure

This is a simple move of Python code that wraps common QEMU
functionality, and are used by a number of different tests
and scripts.

By treating that code as a real Python module, we can more easily:
 * reuse code
 * have a proper place for the module's own unittests
 * apply a more consistent style
 * generate documentation

Signed-off-by: Cleber Rosa <[email protected]>
Reviewed-by: Caio Carrara <[email protected]>
Reviewed-by: Stefan Hajnoczi <[email protected]>
Message-Id: <20190206162901[email protected]>
Signed-off-by: Cleber Rosa <[email protected]>