python/aqmp: handle asyncio.TimeoutError on execute()

python/aqmp: handle asyncio.TimeoutError on execute()

This exception can be injected into any await statement. If we are
canceled via timeout, we want to clear the pending execution record on
our way out.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Beraldo Leal <bleal@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>