samples/net: Add network-related functions to NATS Publisher

- Add TCP/IPv4 routines to this sample.
- Add a testcase.ini file.

This NATS sample code demonstrates how to implement a NATS publisher
application.

Change-Id: Ifeac3bf03b7febafcee927b1d2ec256685885fd8
Signed-off-by: Flavio Santes <flavio.santes@intel.com>