qemu|qtest: Avoid dangerous arguments

The list object is mutable in python and potentially might modify other
object's arguments when used as default argument. Reproducer:

    >>> vm1 = QEMUMachine("qemu")
    >>> vm2 = QEMUMachine("qemu")
    >>> vm1._wrapper.append("foo")
    >>> print vm2._wrapper
    ['foo']

In this case the `args` is actually copied so it would be safe to keep
it, but it's not a good practice to keep it. The same issue applies in
inherited qtest module.

Signed-off-by: Lukáš Doktor <ldoktor@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-Id: <20170818142613.32394-3-ldoktor@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/scripts/qtest.py b/scripts/qtest.py
index d5aecb5f49..ab183c0635 100644
--- a/scripts/qtest.py
+++ b/scripts/qtest.py
@@ -79,7 +79,7 @@ class QEMUQtestProtocol(object):
 class QEMUQtestMachine(qemu.QEMUMachine):
     '''A QEMU VM'''
 
-    def __init__(self, binary, args=[], name=None, test_dir="/var/tmp",
+    def __init__(self, binary, args=None, name=None, test_dir="/var/tmp",
                  socket_scm_helper=None):
         if name is None:
             name = "qemu-%d" % os.getpid()