samples/net/http: Add the HTTP client sample application

This patch adds a basic HTTP client sample application.
The following HTTP 1.1 methods are supported: GET, HEAD,
OPTIONS and POST.

This sample application does not define an API for HTTP,
for more information see ZEP-346.

Jira: ZEP-827

Change-Id: Iee63a53f2ef424964f040eba20326d648249fc24
Signed-off-by: Flavio Santes <flavio.santes@intel.com>