fish: '-i' option automatically handles whole-disk encryption.

fish: '-i' option automatically handles whole-disk encryption.

This feature is also available in guestmount because of the
shared option parsing code.

You don't need to do anything to enable it, just using -i
will attempt decryption of encrypted partitions.

Only works for simple Fedora whole-disk encryption.  It's a
work-in-progress to make it work for other types of encryption.