Update rpc/impl_qpid.py from oslo

The current qpid driver cannot serialize objects containing strings
longer than 65535 characters.  This just became a breaking issue when
the message to scheduler_run_instance went over that limit.  The fix has
been commited to oslo, so this just syncs it over to Nova.

Bug 1175808
Bug 1187595

Change-Id: If95c11a7e03c81d89133f6cad0dcbb6d8acb8148
Merge "Update rpc/impl_qpid.py from oslo"