used ISO is not unmounted

[pirat89]

In case the ISO is used, the mountpoint under /tmp directory is created. However, after the r-u-t is done,
the mountpoint is not unmounted. With new run of r-u-t is created another new mountpoint, etc. Even in case of use the --clean option, the mountpoints are still mounted. The r-u-t should unmount the iso, when it is done to not mess the system.