Fix GRUB for for precise
Fix GRUB for for precise

    --target param is not supported in precise

Change-Id: Ie369ed9d53dbb462cf253144251da4d5c463107c
Fixes: bug #1175275

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