samples/net: Add a NATS subscriber application

This sample code demonstrates how to write a NATS subscriber
application. Code is self-documented and a README file is also
included.

This sample code uses the netz API.

The NATS protocol specification is available at:
http://nats.io/documentation/internals/nats-protocol/



Origin: Original

Jira: ZEP-415
Jira: ZEP-573
Jira: ZEP-597

Change-Id: I4b7e56bb6c2a934012b33039ea5b313b14f3b4c5
Signed-off-by: Flavio Santes <flavio.santes@intel.com>