block: qemu-iotests - update 085 to use common.qemu

block: qemu-iotests - update 085 to use common.qemu

The new functionality of common.qemu implements the QEMU control
and communication functionality that was originally in test 085.

This removes that now-duplicate functionality, and uses the
common.qemu functions.

The QEMU commandline changes slightly due to this; in addition to
monitor and qmp i/o options, the new QEMU commandline from inside
common.qemu now introduces -machine accel=qtest.

Reviewed-by: Benoit Canet <benoit@irqsave.net>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Jeff Cody <jcody@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>