Beautify the image creation output

 * Mount silently when mounting ro
 * Add a warning if no inspection method is available
 * In Windows put the "Preparing system for image creation" before
   mounting takes place
windows: Simplify the VM boot monitoring code

There is no need to use PowerShell to write the random token to the
serial port. Doing 'echo token > COM1' will do the trick.
Minor fixes in the sysprep params menu

 * Use select_file() to update a "file" sysprep param
 * Switch the order of <Details> and <Update> buttons
 * Use the last visited menu entry as default item
Add a new "directory" type for sysprep params