Move dib-run-parts from dib-utils into diskimage-builder directly.
For calling outside the chroot, we provide a standard entry-point
script. However, as noted in the warning comment, the underlying
script is still copied directly into the chroot by the dib-run-parts
element. I believe this to be the KISS approach.
This removes the dependency on dib-utils. We have discussed this
previously and nobody seemed to think retiring dib-utils was going to
be an issue.
This also updates the documentation to not mention dib-utils, or using
disk-image-create via $PATH setup, but rather gives instructions on
installing from pip with a virtualenv.
Change-Id: Ic1e22ba498d2c368da7d72e2e2b70ff34324feb8
