cgnat test case added

cgnat test case added

A cgnat test can now be executed. This test needs 3 PROX instances. The
first one, the generator needs to have an interface on the private
dataplane network. The second instance, the cgnat needs to have it's
first dataplane interface on the private network, while the second data
plane needs to be on the public network. The third instance will be
playing the role of internet server that the generator is connecting to.
It will have one dataplane interface on the public network. This third
instance will increase the packet size of the received packets by
padding it with zeros and it will send the packets back to the cgnat
mutliple times. How many times is defined by a multiplier in the
cgnat.cfg file.
In that cgnat file, we also define a range of IP addresses that will be
used for the dynamic source IP NAT-ing. Make sure that the ports are
allowed to accept other IP addresses than their own (e.g. allowed
address pairs) and that the range of IP addresses is not overlapping
with other machines in the public network.

Change-Id: Ibc1c8513ac4e8a304378814fceb28c090dff895f
Signed-off-by: Luc Provoost <luc.provoost@intel.com>