NetconfClientDispatcher moved to constructor arguments in NetconfClient
This way NioEventLoopGroup instance can be reused by multiple clients.
Dispatcher created in NetconfCLient's constructor spawned an instance of NioEventLoopGroup (in AbstractDispatcher in bgpcep repo).
Instance of NioEventLoopGroup spawns new threads and with multiple concurrent clients system could get out of resources e.g. Too many open files, Unable to create new native thread.
Change-Id: I7dffed243d62ea0be4786d067a16d4e58ab1530c
Signed-off-by: Maros Marsalek <mmarsale@cisco.com>