NAT44ed: Add pure throuhput bidir tests

+ With ramp-up, without reset, with session verification.
+ Uses the same profile as pps tests.
+ Ramp up duration is not specified, as duration is computed.
+ Timeout tracking with automated ramp-up.
 + Correct computation of next duration.
 + Checking both early and late sessions.
 + No loss measurement also acts as a ramp-up.
+ Return ReceiveRateMeasurement from send_traffic_on_tg_internal,
  as that is needed for detecting whether trial is ok as ramp up.
- Udp needs quite low ramp-up rate after recent regression.
 - Max scale has higher rate (so failing) to avoid session timeouts.
+ Bump copyright year.

Change-Id: I50c928659cd5b985b490a2e5fb69c5cd790600b0
Signed-off-by: Vratko Polak <vrpolak@cisco.com>