Allow to disable default gw feature

- Default gateway is a good feature for having host discovery, and
  consequently hosts' pings, work out of the box.
  But in real scenarios a controlled network node may be connected to a
  legacy switch's trunk port which exposes thousand of hosts which ARP
  packets would easily stress controller functionality.
  Even though today this can be prevented by configuring a more
  specific subnet gateway, the issue is very much possible at first
  controller boot, and can always re-occur during subnet config manipulation
  if at any point of time we have no user configured subnet gateways.
- This patch provides a way to disable he default gw feature by mean of
  a property in config.ini. Property addition is not included, current
  behavior is unchanged.

Change-Id: I15b63233e3ed46a8a9fb57bb0988a0d4a2984b11
Signed-off-by: Alessandro Boch <aboch@cisco.com>
BUG-848 Fix netconf communication while using CHUNK encoding

Cause:
When using Chunk encoding, the negotiation process lasts longer due to pipeline manipulation.
Messages received while still in negotiation were not processed correctly (This is incorrect, messages should not be processed while still in negotiation).

Fix:
Introduce a message barrier that will forward only hello message until negotiation is completed (implemented in NetconfXmlToHelloMessageDecoder).
Modify SessionNegotiators to replace message barier/hello decoder when negotiation is finished and to process non-hello messages stopped by the barier.

* Exclude pax-url-aether dependency in netconf-it

Change-Id: Ifa0a97da75ac3cdca29e29bf40138b637e08ff45
Signed-off-by: Maros Marsalek <mmarsale@cisco.com>
BUG-848 Make base capabilities from netconf server configurable

Refactor ConcurrentClientsTest, add cases for different netconf server configuration (EXI/CHUNK)

Change-Id: Ie84ea1ff716b11b0da49e0498127a0defc86f41f
Signed-off-by: Maros Marsalek <mmarsale@cisco.com>
Merge "Allow to disable default gw feature"
Merge changes Ie84ea1ff,Ifa0a97da

* changes:
  BUG-848 Make base capabilities from netconf server configurable
  BUG-848 Fix netconf communication while using CHUNK encoding