NGI Assure project: Probabilistic NAT Traversal

Implementation details milestone 1

See revision 4b2303a on branch dev/t3ss/probnatt

src/service/transport/nat_router.shTest framework router component to fake kernel behavior to keep a port of an outgoing connection open.
scripts/netjail/nat_node_test.shTest script to just send test messages to another node to open up a port.
scripts/netjail/getmsg.shTest script to receive test messages from nat_node_test.sh.
test_transport_plugin_cmd_nat_mapping.cTestcase to start the script which sends test messages to open up ports.
test_transport_nat_mapping_topo.confConfiguration for the test case.
test_transport_nat_mapping.shScript to start the test case.
scripts/Makefile.amAdded nat_node_test.sh and getmsg.sh.
scripts/netjail/netjail_start.shAdded node nummber parameter to node start script, and make the script run in background.
scripts/netjail/netjail_stop.shAdded node nummber parameter to node stop script.
src/service/testing/testing_api_cmd_exec_bash_script.cBugfixing the script that was initially implemented to do explorative testing of transport integrsation, and which is now also used to start the script which sends test messages.
src/service/transport/Makefile.amAdded test_transport_plugin_cmd_nat_mapping.c