Ensure context type is handled when using to_dict

Handle the case where the context passed into def pack_context() is a
dictionary. If a dictionary is passed in, we don't need to call to_dict
before updating the msg.

fixes bug 1208971

Change-Id: I2ce0b28f97634e717868e0ee5525189338d4981c
Merge "Ensure context type is handled when using to_dict"