use ament_python_install_package when package is not installed

[knorth55]

this PR fix #141 with this PR, we can use rosidl_generator_interfaces and ament_python_install_package in the same CMakeLists.txt.

But the order is important. as https://github.com/ros-drivers/audio_common/pull/212, we need to ament_python_install_package first and rosidl_generate_interfaces later.

ament_python_install_package(${PROJECT_NAME})

rosidl_generate_interfaces(${PROJECT_NAME}
  ${msg_files}
  ${action_files}
  DEPENDENCIES
    action_msgs
    audio_common_msgs
    builtin_interfaces
)