Unittest
Add tests for re6setnet, slapos!1165 (closed) use this to run test on test-node.
tests contain 2 parts: unittest and network simulate test
-unittest: contain test for RegistryServer, RegistryClient, cli.conf, tunnel.BaseTunnelManger, tunnel.MultGatewayManager zf.huang/re6stnet@e7636b86
-net_test: use nemu to create net namespaces and run registry or node in each net ns, finally use ping to test ipv6 connectivty zf.huang/re6stnet@5bc6419c