mrd_test_unit_ready - Verify a medium changer is ready to accept
    commands

    Windows NT         mrd.dll
    UNIX               /usr/lib/libmrd.a
    OpenVMS            MRD$RTL.EXE

    #include <mrd_common.h>
    #include <mrd_message.h>

    int mrd_test_unit_ready(
        robot_info_t *robot_info,
        dev_status_t *dev_status);