Modify relative paths of lib, elements for packaging

(Based on review https://review.openstack.org/#/c/36009)

Scripts test for existence of ../share/diskimage-builder and
fall-back to ../ if not found. This allows scripts to run unmodified
from a packaged installation or a local archive/repository.

Change-Id: I0cf4c1fdb8e42ec284c56860cb15818632b93b9e
Merge "Modify relative paths of lib, elements for packaging"