Merge pull request #78 from changbl/working

Skip leader election if zookeeper storage is not available
Fix bugs to make multi-datacenter work
Wrap ip_to_mac and mac_to_ip into class ArpMapping
Decouple mac_to_vmac from mac_to_position
Add class TenantManager to manage tenant information
Fix bugs to make live migration work
Merge pull request #79 from powerist/bugfix

Fix bugs to make multi-datacenter work
Bug fixed for single switch migration
Merge pull request #80 from powerist/working

Bug fixed for single switch migration
Fix live migration bugs
Merge pull request #81 from powerist/working

Fix live migration bugs
Live migration: add timeout to the flow from vmac_old to vmac_new
Merge pull request #82 from powerist/migration

Live migration: add timeout to the flow from vmac_old to vmac_new
Reform data structure

Add class VmManager, SwcManager, RpcManager and ArpManager
vm_id generation

Use queue to generate unique vm_id for each VM.
Merge pull request #83 from powerist/failover

Code refinement
add arp test scripts from Pingkai, with modifications and fixes