fish: Implement progress bars in guestfish.

fish: Implement progress bars in guestfish.

The progress bar is updated 3 times per second, and is not displayed
at all for operations which take less than two seconds.

You can disable progress bars by using the flag --no-progress-bars,
and you can enable progress bars in non-interactive sessions with
the flag --progress-bars.

A good way to test this is to use the following command:

guestfish --progress-bars \
          -N disk:10G \
          zero-device /dev/sda

(adjust "10G" to get different lengths of time).