This could result in the network plugin not retrieving the pod ip in a
call to SyncPod when using the `exec` network plugin.
The CNI and kubenet network plugins ignore the name/namespace arguments,
so they are not impacted by this bug.
I verified the second included test failed prior to correcting the
argument order.
Fixes#29161
Use the generic runtime method to get the netns path. Also
move reading the container IP address into cni (based off kubenet)
instead of having it in the Docker manager code. Both old and new
methods use nsenter and /sbin/ip and should be functionally
equivalent.