Merge pull request #34 from changbl/working

Two minor naming changes
Unfinished multi-datacenter ARP

This version is unfinished.
Commit first so that Changbin can do code review.
Merge pull request #36 from powerist/working

Multi-datacenter ARP
Add local cache for network data
Merge pull request #37 from powerist/working

Add local cache for network data
Multi-datacenter ARP:

1. ARP received by controller 1.
2. Local look-up.
3. Send arp reply to requesting node.
4. If requested node is local, set up
intra-datacenter flows.
5. If requested node is in another datacenter
which is controlled by controller 2,
set up inter-datacenter flows locally,
and use rpc to instruct controller 2 to
set up inter-datacenter flows.
Merge pull request #38 from powerist/working

Multi-datacenter ARP
Clean up code:

Add function set_unicast_flow
Merge pull request #39 from powerist/working

Clean up code:
Add transaction to rpc
Merge pull request #40 from powerist/working

Add transaction to rpc
Add function update_arp_mapping
Merge pull request #41 from powerist/working

Add function update_arp_mapping
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
Code improvement

Include naming, format, comments, TODOs, config_options

Did not touch functionality part except DHPC module