Merge pull request #1 from safchain/service_instance

vrouter agent service instance SNAT script support
Split out namespace management

Change-Id: I1e3484b6e3bb95b427aa0b738de718a8bac9268b
Add async start of the netns_command script

Change-Id: Id8b3ad7f06a13acdb49b971733b7732eb7fa6811