VPP-895 multi-thread: fix vpp crash on show runtime

VPP-895 multi-thread: fix vpp crash on show runtime

In multi-threaded model (e.g. 1 main and 1 worker threads),
after an ethernet interface is deleted (e.g. vhost-user interface),
'show runtime' command produces garbled output and sometimes
leads to vpp crash.

The reason is because vlib_node_rename() frees and reallocates node's
'n->name' vector, however the change is not propagated into copies
of the node on worker threads.

Change-Id: Ibf22422913b7f2df22f70f3b2fe8dafd34c1dd06
Signed-off-by: Igor Mikhailov (imichail) <imichail@cisco.com>