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 changes Ie84ea1ff,Ifa0a97da

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