the problem of modules start sequence for dragonflow

[hujie]

In current senario when dragonflow local controller start up, there are some problems:
1. dragonflow local controller will first set-controller for openvswitch, and then start openflow controller listening at port 6633, and then start each app one by one, this sequence has the danger that miss openflow messages when the apps start up too late;
2. it has the same problem between the ovsdb monitor module and apps;

So in order to avoid above problems, we should change the module start sequence when dragonflow local controller start up, for example, we should start topology module and apps first, and then start openflow listening, and start ovsdb monitor last.