Join shim into nslistener network ns and end pod support

[WeiZhang555]

runv shim should share same network namespace with nslistener, then if
user try to insert an network interface into runv shim's netns,
nslistener can observe the changes and copy the configure into VM.

Signed-off-by: Zhang Wei zhangwei555@huawei.com

[WeiZhang555]

This is a replacement of #523

[WeiZhang555]

$ ps -ef | grep shim | grep runv
root     20653 28460  0 17:27 ?        00:00:00 docker-containerd-shim 26036710137bfa57b9521adc6a4f206ce9cd3e65292d0f56dfea71bdf18e1245 /var/run/docker/libcontainerd/26036710137bfa57b9521adc6a4f206ce9cd3e65292d0f56dfea71bdf18e1245 /usr/local/bin/runv
root     20836 20653  0 17:27 ?        00:00:00 runv --root /run/runv --log_dir /var/log/hyper/shim-26036710137bfa57b9521adc6a4f206ce9cd3e65292d0f56dfea71bdf18e1245 --debug --log /tmp/runv.log --log-format json shim --container 26036710137bfa57b9521adc6a4f206ce9cd3e65292d0f56dfea71bdf18e1245 --process init --proxy-exit-code --proxy-signal --proxy-winsize
$ sudo ls -l /proc/20836/ns/net
lrwxrwxrwx 1 root root 0 Jun 30 17:35 /proc/20836/ns/net -> net:[4026532302]
$ ps -ef | grep nslistener
root     20695 20666  0 17:27 ?        00:00:00 containerd-nslistener
zhangwei 21859  2224  0 17:35 pts/28   00:00:00 grep --color=auto nslistener
$ sudo ls -l /proc/20695/ns/net
lrwxrwxrwx 1 root root 0 Jun 30 17:27 /proc/20695/ns/net -> net:[4026532302]

[WeiZhang555]

Append a new commit to enable POD support.

[gnawux]

@WeiZhang555 Having merged #537, do we still need this?

[laijs]

#537 reuses your code (nsenter/) thanks. @WeiZhang555

#537 does not include the support of --net container:xxx. please update it