STORM-155: Storm rebalancing code causes multiple topologies assigned to a single port

Retrying synchronize-supervisor if assignments read was inconsistent before throwing RuntimeException in order to avoid supervisor crash as possible.
It would be nice to include some text to the effect that we are retrying "1 of 3" times in addition to this stack trace, just to avoid confusing this with a more serious error.  But this is very, very minor.