iotest: fix python based IO tests

iotest: fix python based IO tests

The previous commit refactoring iotests.py:

  commit 66613974468fb6e1609fb3eabf55981b1ee436cf
  Author: Daniel P. Berrange <berrange@redhat.com>
  Date:   Wed Jul 20 14:23:10 2016 +0100

    scripts: refactor the VM class in iotests for reuse

was not properly tested and included a number of broken
bits.

 - The 'event_match' method was not moved into qemu.py
 - The 'self._args' list parameter in QEMUMachine needs
   to be copied otherwise modifications will affect the
   global 'qemu_opts' variable in iotests.py
 - The QEMUQtestMachine class methods had inverted
   parameter order for the super() calls
 - The QEMUQtestMachine class forgot to add
   '-machine accel=qtest'
 - The QEMUQtestMachine class constructor needs to set
   a default 'name' value before using it as it may
   be None
 - The QEMUQtestMachine class constructor needs to use
   named parameters when calling the super constructor
   as it is leaving out some positional parameters.
 - The 'qemu_prog' variable should be a string not a
   list in iotests.py
 - The VM classs constructor needs to use named
   parameters when calling the super constructor
   as it is leaving out some positional parameters.
 - The path to the socket-scm-helper needs to be
   passed into the QEMUMachine class

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 1469549767-27249-1-git-send-email-berrange@redhat.com
Signed-off-by: Max Reitz <mreitz@redhat.com>