python/qemu/machine: QEMUMachine: improve qmp() method

We often call qmp() with unpacking dict, like qmp('foo', **{...}).
mypy don't really like it, it thinks that passed unpacked dict is a
positional argument and complains that it type should be bool (because
second argument of qmp() is conv_keys: bool).

Allow passing dict directly, simplifying interface, and giving a way to
satisfy mypy.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-Id: <20210824083856.17408-25-vsementsov@virtuozzo.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>