sysprep: Disable fs-uuids operation by default.

Disable this operation because it is more likely than not to break
Linux guests.

To fix this properly will involve finding all the places in the guest
where the UUIDs are used to locate and mount filesystems,
eg. /etc/fstab and possibly initramfs.

This updates commit 8965368eb89532ac1613fffb0a3a661f005bae81.
sysprep: Allow root and non-root passwords to be set.

This adds a virt-sysprep 'password' operation which adds the
following command line options:

  --root-password     Set the guest's root password.
  --password          Set any guest password.