mark vif_driver as deprecated and log warning

Several classes were dropped from nova.virt.libvirt.vif from havana ->
icehouse, leading to invalid configurations if one of these classes was
used in the libvirt_vif_driver setting in nova.conf.  The error message
produced by nova-compute in this situation is misleading.

This patch introduces stubs for all of the classes that were removed.
These stubs inherit from LibvirtGenericVIFDriver and log a deprecation
warning in __init__.

This patch also marks the vif_driver option as deprecated.

Change-Id: I6d6cb9315ce6f3b33d17756bcdc77dccda26fefe
Closed-bug: 1302796

nova/virt/libvirt/driver.py

@@ -183,7 +183,9 @@ libvirt_opts = [
                deprecated_group='DEFAULT'),
     cfg.StrOpt('vif_driver',
                default='nova.virt.libvirt.vif.LibvirtGenericVIFDriver',
-               help='The libvirt VIF driver to configure the VIFs.',
+               help='DEPRECATED. The libvirt VIF driver to configure the VIFs.'
+                    'This option is deprecated and will be removed in the '
+                    'Juno release.',
                deprecated_name='libvirt_vif_driver',
                deprecated_group='DEFAULT'),
     cfg.ListOpt('volume_drivers',

nova/virt/libvirt/vif.py

@@ -796,3 +796,36 @@ class LibvirtGenericVIFDriver(LibvirtBaseVIFDriver):
         else:
             raise exception.NovaException(
                 _("Unexpected vif_type=%s") % vif_type)
+
+# The following classes were removed in the transition from Havana to
+# Icehouse, but may still be referenced in configuration files.  The
+# following stubs allow those configurations to work while logging a
+# deprecation warning.
+
+
+class _LibvirtDeprecatedDriver(LibvirtGenericVIFDriver):
+    def __init__(self, *args, **kwargs):
+        LOG.warn('VIF driver \"%s\" is marked as deprecated and will be '
+                 'removed in the Juno release.',
+                 self.__class__.__name__)
+        super(_LibvirtDeprecatedDriver, self).__init__(*args, **kwargs)
+
+
+class LibvirtBridgeDriver(_LibvirtDeprecatedDriver):
+    pass
+
+
+class LibvirtOpenVswitchDriver(_LibvirtDeprecatedDriver):
+    pass
+
+
+class LibvirtHybridOVSBridgeDriver(_LibvirtDeprecatedDriver):
+    pass
+
+
+class LibvirtOpenVswitchVirtualPortDriver(_LibvirtDeprecatedDriver):
+    pass
+
+
+class NeutronLinuxBridgeVIFDriver(_LibvirtDeprecatedDriver):
+    pass