In order for hypervisor based container runtimes to be able to
fully prepare their pod virtual machines networking interfaces,
this patch sets the pod networking namespace before creating the
sandbox container.
Once the sandbox networking namespace is prepared, the runtime
can scan the networking namespace interfaces and build the pod VM
matching interfaces (typically TAP interfaces) at pod sandbox
creation time. Not doing so means those runtimes would have to
rely on all hypervisors to support networking interfaces hotplug.
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>