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.
Thanks for the comment. I updated the code. It shows the message like below now:
```
19102 [nREPL-worker-0] INFO  backtype.storm.daemon.nimbus - Setting new assignment for topology id topology2-2-0: #backtype.storm.daemon.common.Assignment{:master-code-dir "/tmp/bd4c83e2-fcab-44e9-bfd9-678124f22a3f/nimbus/stormdist/topology2-2-0", :node->host {"sup1" "centos63"}, :executor->node+port {[1] ["sup1" 1], [2] ["sup1" 2]}, :executor->start-time-secs {[1] 0, [2] 0}}
19196 [Thread-12] WARN  backtype.storm.daemon.supervisor - Should not have multiple topologies assigned to one port: retrying 1 of 3
19357 [nREPL-worker-0] INFO  backtype.storm.daemon.nimbus - Delaying event :do-rebalance for 0 secs for topology2-2-0
19372 [nREPL-worker-0] INFO  backtype.storm.daemon.nimbus - Updated topology2-2-0 with status {:type :rebalancing, :delay-secs 0, :old-status {:type :active}, :num-workers nil, :executor-overrides {}}
19398 [Thread-12] WARN  backtype.storm.daemon.supervisor - Should not have multiple topologies assigned to one port: retrying 2 of 3
```