python: qemu: add timer parameter for qmp.accept socket

python: qemu: add timer parameter for qmp.accept socket

Also add a new _qmp_timer field to the QEMUMachine class.

Let's change the default socket timeout to None, so that if
a subclass needs to add a timer, it can be done by modifying
this private field.

At the same time, restore the timer to be 15 seconds in iotests.py, to
give an upper bound to the QMP monitor test command execution.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Acked-by: John Snow <jsnow@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Message-Id: <20210809090114.64834-2-eesposit@redhat.com>
Signed-off-by: Hanna Reitz <hreitz@redhat.com>