VM migration:

We define two types of flow adjustment:
1. Same switch migration:
(dpid, port_old, mac) -> (dpid, port_new, mac)

- Modify flow at dpid towards mac.

2. Different switch migration
(dpid_old, port_old, mac) ->
	(dpid_new, port_new, mac):

- Install/Update a new flow at dpid_new towards mac.
- Redirect all flows on dpids
other than dpid_new towards mac.
Merge pull request #42 from powerist/working

VM migration