We replace the base resolv.conf with an "outside" copy so that
resolving works when we're in the chroot.
Installing resolvconf package modifies the in-chroot resolv.conf to a
symlink (to /var/run) which it wants maintained in the final image.
We have the existing "immutable" check for a created resolv.conf file,
but no eqivalent for a symlink.
This adds a check to see if the resolv.conf is a symlink and leave it
alone if it is, assuming it has been re-created in the chroot.
I have tested this with ubuntu-minimal+resolvconf with
dhcp-all-interfaces and the system seems to work with resolvconf
working correctly.
Change-Id: Idd5a26e9d55979bd951577d5b098ed4bfba91ad3
5fa6e3e13c