quantum server shouldn't return tracebacks to clients

Currently, the Quantum server returns exceptions tracebacks to the client. This exposes information about a software issue, as well as what plugin is in use and potentially how it is configured to tenant. This is really none of the tenant's business.

We should log the traceback in the server logs, but then return a generic error to the tenant.

Here's an example of what I got back as a client:

(http://paste.ubuntu.com/960965/ has a pretty-printed version of the traceback below)
danwent@ubuntu:~/quantum$ quantum create_net default net1
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/python_quantumclient-2012.2-py2.7.egg/quantum/client/cli_lib.py", line 275, in create_net
    res = client.create_network(data)
  File "/usr/local/lib/python2.7/dist-packages/python_quantumclient-2012.2-py2.7.egg/quantum/client/__init__.py", line 145, in with_params
    ret = self.function(instance, *args)
  File "/usr/local/lib/python2.7/dist-packages/python_quantumclient-2012.2-py2.7.egg/quantum/client/__init__.py", line 423, in create_network
    return self.post(self.networks_path, body=body)
  File "/usr/local/lib/python2.7/dist-packages/python_quantumclient-2012.2-py2.7.egg/quantum/client/__init__.py", line 384, in post
    headers=headers, params=params)
  File "/usr/local/lib/python2.7/dist-packages/python_quantumclient-2012.2-py2.7.egg/quantum/client/__init__.py", line 305, in do_request
    self._handle_fault_response(status_code, data)
  File "/usr/local/lib/python2.7/dist-packages/python_quantumclient-2012.2-py2.7.egg/quantum/client/__init__.py", line 228, in _handle_fault_response
    EXCEPTION_HANDLERS[self.version](status_code, des_error_body)
  File "/usr/local/lib/python2.7/dist-packages/python_quantumclient-2012.2-py2.7.egg/quantum/client/__init__.py", line 119, in exception_handler_v11
    raise exceptions.QuantumClientException(message=msg)
uantumClientException: 500-{'message': 'Traceback (most recent call last):\n File "/usr/lib/python2.7/dist-packages/eventlet/wsgi.py", line 336, in handle_one_response\n result = self.application(self.environ, start_response)\n File "/usr/lib/python2.7/dist-packages/paste/urlmap.py", line 203, in __call__\n return app(environ, start_response)\n File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 159, in __call__\n return resp(environ, start_response)\n File "/usr/lib/pymodules/python2.7/routes/middleware.py", line 131, in __call__\n response = self.app(environ, start_response)\n File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 159, in __call__\n return resp(environ, start_response)\n File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 159, in __call__\n return resp(environ, start_response)\n File "/usr/lib/pymodules/python2.7/routes/middleware.py", line 131, in __call__\n response = self.app(environ, start_response)\n File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 159, in __call__\n return resp(environ, start_response)\n File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 147, in __call__\n resp = self.call_func(req, *args, **self.kwargs)\n File "/usr/local/lib/python2.7/dist-packages/webob/dec.py", line 208, in call_func\n return self.func(req, *args, **kwargs)\n File "/home/danwent/quantum/quantum/wsgi.py", line 748, in __call__\n action_result = self.dispatch(request, action, args)\n File "/home/danwent/quantum/quantum/wsgi.py", line 780, in dispatch\n return controller_method(request=request, **action_args)\n File "/home/danwent/quantum/quantum/api/api_common.py", line 108, in the_func\n return func(*args, **kwargs)\n File "/home/danwent/quantum/quantum/api/networks.py", line 134, in create\n **body)\n File "/home/danwent/quantum/quantum/plugins/sample/SamplePlugin.py", line 211, in create_network\n new_net = db.network_create(tenant_id, net_name)\n File "/home/danwent/quantum/quantum/db/api.py", line 119, in network_create\n session.flush()\n File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 1559, in flush\n self._flush(objects)\n File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/session.py", line 1630, in _flush\n flush_context.execute()\n File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/unitofwork.py", line 331, in execute\n rec.execute(self)\n File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/unitofwork.py", line 475, in execute\n uow\n File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/orm/mapper.py", line 2264, in _save_obj\n execute(statement, multiparams)\n File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1405, in execute\n params)\n File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1538, in _execute_clauseelement\n compiled_sql, distilled_params\n File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1646, in _execute_context\n context)\n File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/base.py", line 1639, in _execute_context\n context)\n File "/usr/local/lib/python2.7/dist-packages/sqlalchemy/engine/default.py", line 330, in do_execute\n cursor.execute(statement, parameters)\nOperationalError: (OperationalError) no such table: networks u\'INSERT INTO networks (uuid, tenant_id, name, op_status) VALUES (?, ?, ?, ?)\' (\'ee799487-7335-4712-b52b-10f7dd748d7a\', u\'default\', u\'net1\', \'UNKNOWN\')\n'}