bug fixes, integration tests for metadata

common/cpp/include/common/error.h

common/cpp/include/common/io_error.h

common/cpp/include/database/database.h

common/cpp/include/database/db_error.h

common/cpp/include/unittests/MockDatabase.h

common/cpp/src/database/database.cpp

common/cpp/src/database/mongodb_client.cpp

common/cpp/src/system_io/system_io_linux_mac.cpp

...ples/producer/dummy-data-producer/dummy_data_producer.cpp

examples/worker/getnext_broker/getnext_broker.cpp

examples/worker/getnext_broker_python/check_linux.sh

examples/worker/getnext_broker_python/check_windows.bat

examples/worker/getnext_broker_python/getnext.py

producer/api/src/producer_impl.cpp

producer/api/src/request_handler_tcp.cpp

producer/api/unittests/test_producer_impl.cpp

producer/api/unittests/test_request_handler_tcp.cpp

.../event_monitor_producer/src/system_folder_watch_linux.cpp

receiver/src/requests_dispatcher.cpp

receiver/unittests/test_requests_dispatcher.cpp