Get rid of nsenter and socat

[Random-Liu]

Currently we are using nsenter for both CNI plugin and port forword.

Ideally, we should be able to use NetNS.Do to run code inside a specific network namespace.

However, golang has an issue that it may spawn new threads from locked thread, which will inherit the network namespace. golang/go#20676

We should be able to get rid of all nsenters after this is fixed.

[Random-Liu]

Also ref #139.

[abhi]

The other option would be to use ip netns exec provided we have our network namespaces created under /var/run/netns/....
Looks like there is bug open pointing issues with usage of ip netns exec https://bugzilla.redhat.com/show_bug.cgi?id=882047

[cpuguy83]

Or alternatively could setup a container to do this work... of course any option still requires execing a new process until go1.10 lands.

[Random-Liu]

golang 1.10 is released, golang/go#20676 should have been fixed.

We can get rid of nsenter and socat after switch to golang 1.10.

[tkellen]

🎉