Add support for SSH (Secure Shell) block device.
fish: options: Whitespace change.
fish: Add -a URI (add remote storage) to options.

Add a remote drive by doing:

 guestfish -a ssh://example.com/path/to/disk.img

There are several different protocols supported, as explained in the
man page.

This affects all virt-* tools that use the common guestfish options
parsing code.