Merge pull request #83 from powerist/failover

Code refinement
add arp test scripts from Pingkai, with modifications and fixes
Merge pull request #84 from changbl/working

add arp test scripts from Pingkai, with modifications and fixes
Merge pull request #85 from powerist/failover

New failover
parallelize arp scripts to speedup
Merge pull request #86 from changbl/working

parallelize arp scripts to speedup
Merge pull request #87 from powerist/failover

Gateway high availability
Failover bug