Make the finalise_base function less Ubuntu-ish.
Make the finalise_base function less Ubuntu-ish.

The finalise_base function was creating a broken link at /etc/resolv.conf
when building a non ubuntu image.

Change-Id: I974d43fd6db365dbff9c85195e3b72950f3409da

switch-ch/diskimage-builder,openstack/diskimage-builder,citrix-openstack-build/diskimage-builder,rdo-management/diskimage-builder,NaohiroTamura/diskimage-builder,varunarya10/diskimage-builder,rdo-management/diskimage-builder,switch-ch/diskimage-builder,varunarya10/diskimage-builder,zioproto/diskimage-builder,JioCloud/diskimage-builder,takahashinobuyuki/diskimage-builder,CSC-IT-Center-for-Science/diskimage-builder,eantyshev/diskimage-builder,citrix-openstack-build/diskimage-builder,CSC-IT-Center-for-Science/diskimage-builder,JioCloud/diskimage-builder,eantyshev/diskimage-builder,openstack/diskimage-builder,takahashinobuyuki/diskimage-builder,zioproto/diskimage-builder,NaohiroTamura/diskimage-builder