Add send socket commands function

Add send socket commands function

Pktgen provides a TCP socket connection to allow the user to control
it from a remote console or program [1].

This new method will provide Yardstick the ability to send string
commands to a port in a remote host.

[1] http://pktgen-dpdk.readthedocs.io/en/latest/socket.html

JIRA: YARDSTICK-1186

Change-Id: I9d64ccad662fa3599de65654c5dab02833fcc91d
Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>