config: cannot create virtual-network in default-domain in keystone v3 mode

When keystone v3 is used, the default domain id in contrail is tracked to match with 'default' in keystone in OpenstackDriver object which should be a singleton.

However the ResourceApiDriver class instead of using this singleton constructs another instance of OpenstackDriver and then loses the value of _vnc_default_domain_id leading to a traceback on network create of:

Traceback (most recent call last):
  File "/opt/contrail/api-venv/lib/python2.7/site-packages/stevedore/extension.py", line 171, in _invoke_one_plugin
    response_callback(func(e, *args, **kwds))
  File "/opt/contrail/api-venv/lib/python2.7/site-packages/stevedore/extension.py", line 145, in _call_extension_method
    return getattr(extension.obj, method_name)(*args, **kwds)
  File "/opt/contrail/api-venv/lib/python2.7/site-packages/vnc_openstack/__init__.py", line 612, in pre_project_read
    self._openstack_drv.sync_project_to_vnc(id)
  File "/opt/contrail/api-venv/lib/python2.7/site-packages/vnc_openstack/__init__.py", line 256, in _ksv3_sync_project_to_vnc
    proj_obj = vnc_api.Project(project_name, parent_obj=dom_obj)
  File "/usr/lib/python2.7/dist-packages/vnc_api/gen/resource_client.py", line 5107, in __init__
    super(Project, self).__init__(name, parent_obj, quota, id_perms, display_name, *args, **kwargs)
  File "/usr/lib/python2.7/dist-packages/vnc_api/gen/resource_common.py", line 7879, in __init__
    self.parent_type = parent_obj._type
AttributeError: 'str' object has no attribute '_type'

This is because dom_obj is in fact an error message asking for either name or id to be specified.

This can be fixed by using a singleton as below:

--- /opt/contrail/api-venv/lib/python2.7/site-packages/vnc_openstack/__init__.py 2014-09-30 19:38:08.765484124 +0000
+++ vnc_openstack_init.py 2014-09-30 19:34:49.321549842 +0000
@@ -49,8 +49,11 @@
     return (auth_user, auth_passwd, admin_token, admin_tenant, auth_url,
             keystone_sync_on_demand)

+openstack_driver = None
 class OpenstackDriver(vnc_plugin_base.Resync):
     def __init__(self, api_server_ip, api_server_port, conf_sections):
+ global openstack_driver
+ openstack_driver = self
         self._vnc_api_ip = api_server_ip
         self._vnc_api_port = api_server_port

@@ -481,7 +484,7 @@
          self._keystone_sync_on_demand) = get_keystone_opts(conf_sections)

         self._vnc_lib = None
- self._openstack_drv = OpenstackDriver(api_server_ip, api_server_port, conf_sections)
+ self._openstack_drv = openstack_driver
         # Tracks which domains/projects have been sync'd from keystone to contrail api server
         self._vnc_domains = set()
         self._vnc_projects = set()