Use dib-run-parts from dib-utils

Now that dib-run-parts has been moved to the dib-utils project, we
need to update diskimage-builder to use it instead of the version
directly in diskimage-builder.

This change removes the old copy of the dib-run-parts script in
the element, adds dib-utils as a dependency of diskimage-builder,
and updates the uses of dib-run-parts to correctly handle the fact
that it is now external to the project.

Requires I0be1f876d0e4a7d38e0d5c6010a552a8ebb158a4

Change-Id: Ia0a0df7784a14c49b5c47ac0b03e6c2602c84b3b
Merge "Use dib-run-parts from dib-utils"