virt-sysprep: Switch to using guestmount, add more features.

virt-sysprep: Switch to using guestmount, add more features.

This switches virt-sysprep to use guestmount instead of guestfish.
This makes the script a little bit easier to modify for sysadmins.

This commit also adds:

 - dhcp-client-state
 - dhcp-server-state
 - logfiles
 - random-seed
 - smolt-uuid
 - yum-uuid

SELinux relabelling, and a section on security in the manual page.