Merge pull request #42 from powerist/working

VM migration
Code improvement

Include naming, format, comments, TODOs, config_options

Did not touch functionality part except DHCP module
Merge pull request #43 from changbl/working

Code improvement
Code fix

Delete DPID_TO_CONNS, DPID_TO_IP, GATEWAY;
Add transactions to RPC;
Delete unused "in_port" in _handle_arp_request;
Delete argument "migration" in update_position;