tests/vm: Let subclasses disable IPv6

The mechanism will be used to work around issues related to IPv6
on the netbsd image builder.
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>
Reviewed-by: NThomas Huth <thuth@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20191018181705.17957-3-ehabkost@redhat.com>
Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>

tests/vm/basevm.py

@@ -57,6 +57,8 @@ class BaseVM(object):
     arch = "#arch"
     # command to halt the guest, can be overridden by subclasses
     poweroff = "poweroff"
+    # enable IPv6 networking
+    ipv6 = True
     def __init__(self, debug=False, vcpus=None):
         self._guest = None
         self._tmpdir = os.path.realpath(tempfile.mkdtemp(prefix="vm-test-",
@@ -81,7 +83,8 @@ class BaseVM(object):
         self._args = [ \
             "-nodefaults", "-m", "4G",
             "-cpu", "max",
-            "-netdev", "user,id=vnet,hostfwd=:127.0.0.1:0-:22",
+            "-netdev", "user,id=vnet,hostfwd=:127.0.0.1:0-:22" +
+                       (",ipv6=no" if not self.ipv6 else ""),
             "-device", "virtio-net-pci,netdev=vnet",
             "-vnc", "127.0.0.1:0,to=20"]
         if vcpus and vcpus > 1: