Revert "p2v: Disable SELinux in virt-p2v-make-disk."

The commit claimed that SELinux was disabled in the
virt-p2v-make-kickstart script, and so this was just making things
consistent.  However this is not true.  SELinux *is* enabled in the
kickstart version.  There is some code to disable it, but it is
commented out (admittedly it's hard to tell because the code is buried
in a multi-line sed expression).

The commit message also claimed (this time correctly) that the
'--selinux-relabel' step caused an extra reboot each time virt-p2v is
run from the ISO.  However we have recently fixed this so it can
usually do the relabelling during the build, not at boot time, so this
is no longer a problem.

This reverts commit 25ffcc7d43.

p2v/virt-p2v-make-disk.in

@@ -170,10 +170,9 @@ EOF
 latest_version="$(cd /lib/modules; ls -1vr | head -1)"
 dracut -f --kver $latest_version
 EOF
-        # Double quotes because we want $tmpdir to be expanded.
-        # Disable SELinux for consistency with virt-p2v-make-kickstart.
+        # Double quotes because we want $tmpdir to be expanded:
         extra_args="
-          --edit /etc/selinux/config:s/^SELINUX=.*/SELINUX=disabled/g
+          --selinux-relabel
           --upload $tmpdir/p2v.conf:/etc/dracut.conf.d/
           --run $tmpdir/post-install
         "