Added unittests to NetworkProducerPeerImpl

common/cpp/include/system_wrappers/has_io.h

common/cpp/src/system_io/has_io.cpp

producer/api/src/producer_impl.cpp

producer/api/unittests/test_producer_impl.cpp

receiver/src/network_producer_peer.h

receiver/src/network_producer_peer_impl.cpp

receiver/src/network_producer_peer_impl.h

receiver/src/network_producer_peer_impl_functions.cpp

receiver/src/network_producer_peer_impl_handlers.cpp

receiver/unittests/test_network_producer_peer_impl.cpp

receiver/unittests/test_receiver.cpp