Added more producer tests

common/cpp/include/system_wrappers/io.h

common/cpp/include/system_wrappers/system_io.h

common/cpp/src/system_io_linux.cpp

producer/api/include/producer/producer.h

producer/api/src/producer_impl.cpp

producer/api/src/producer_impl.h

producer/api/unittests/test_producer_impl.cpp

producer/dummy-event-detector-cpp/src/dummy_detector.cpp

receiver/src/file_refernce_handler.cpp

receiver/src/file_refernce_handler.h

receiver/src/network_producer_peer.cpp

receiver/src/network_producer_peer.h

receiver/src/network_producer_peer_handlers.cpp

receiver/src/receiver.cpp

receiver/src/receiver.h

worker/api/cpp/src/folder_data_broker.cpp

worker/api/cpp/unittests/test_folder_broker.cpp