v2v: Rebuild initrd last.

Old virt-v2v rebuilt the initrd late.  Currently we rebuild the initrd
right after choosing a kernel, but it's best to update the initrd
at the end since mkinitrd may depend on other configuration files
that we are changing (especially see next commit).
v2v: Reconfigure /etc/modprobe.conf (RHBZ#1141145).

More code that was omitted during the translation of old virt-v2v.