Move element-info from a wrapper script to a standard entry-point
console_script.
Update the documentation to explain how to run it for development. I
don't think we should support the idea that you can check-out the code
and run ./bin/disk-image-create -- it has dependencies (dib-utils,
etc) and needs to be run from a virtualenv (this is what CI in the
gate does). A follow-up can clean-up some of the path munging stuff
we have for this in disk-image-create.
Change-Id: Ic0c03995667f320a27ac30441279f3e6abb6bca8
