Add RPC serialization checking, fix exposed problems.

Related to bug 933584.

In this bug, I hit a case where some code tried to send a SQLAlchemy
model over rpc, which failed since it couldn't be serialized by Qpid.
This patch adds a simple serialization check to the fake RPC driver
using json.  It also fixes problems that were exposed by adding this
check.

If json can't serialize a message sent through the fake RPC
driver, it will raise TypeError, causing unit tests to fail.  18 unit
tests failed with the check in place, but it was due to only 2 places
in the compute API.

Change-Id: I63f3077c0fa35097d4f5d2c485f4e48eede2c751

nova/rpc/impl_fake.py

@@ -18,6 +18,7 @@ queues.  Casts will block, but this is very useful for tests.
 """
 
 import inspect
+import json
 import signal
 import sys
 import time
@@ -124,9 +125,16 @@ def create_connection(new=True):
     return Connection()
 
 
+def check_serialize(msg):
+    """Make sure a message intended for rpc can be serialized."""
+    json.dumps(msg)
+
+
 def multicall(context, topic, msg, timeout=None):
     """Make a call that returns multiple times."""
 
+    check_serialize(msg)
+
     method = msg.get('method')
     if not method:
         return
@@ -158,7 +166,7 @@ def cast(context, topic, msg):
 
 
 def notify(context, topic, msg):
-    pass
+    check_serialize(msg)
 
 
 def cleanup():
@@ -167,6 +175,7 @@ def cleanup():
 
 def fanout_cast(context, topic, msg):
     """Cast to all consumers of a topic"""
+    check_serialize(msg)
     method = msg.get('method')
     if not method:
         return