Fix rclpy tests on windows

Python library _rclpy could not be imported due to rclpy_sigint.dll not
being on PATH. This uses 'APPEND_LIBRARY_DIRS' argument to
ament_add_nose_test to add that directory to the path.

Author: sloretz

rclpy/CMakeLists.txt

@@ -146,6 +146,7 @@ if(BUILD_TESTING)
       WORKING_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}"
       PYTHON_EXECUTABLE "${PYTHON_EXECUTABLE}"
       APPEND_ENV AMENT_PREFIX_PATH=${ament_index_build_path}
+      APPEND_LIBRARY_DIRS "$<TARGET_FILE_DIR:rclpy_sigint>"  # Windows add rclpy_sigint.dll to path
       TIMEOUT 90
     )
   endif()