Acceptance tests: work around socket dir

Change 32558ce introduced specific directories for the socket dir
when using python/qemu/machine.py:QEMUMachine.  iotests probably
didn't catch the condition that two simultaneous QEMUMachine
instances, without manually set temporary or socket dirs would clash.

Having two QEMUMachine instances is a condition expected for many
acceptance tests, and it's already used by the migration tests.

Signed-off-by: Cleber Rosa <crosa@redhat.com>

tests/acceptance/avocado_qemu/__init__.py

@@ -11,6 +11,7 @@
 import os
 import sys
 import uuid
+import tempfile
 
 import avocado
 
@@ -69,7 +70,7 @@ def setUp(self):
             self.cancel("No QEMU binary defined or found in the source tree")
 
     def _new_vm(self, *args):
-        vm = QEMUMachine(self.qemu_bin)
+        vm = QEMUMachine(self.qemu_bin, sock_dir=tempfile.mkdtemp())
         if args:
             vm.add_args(*args)
         return vm