Add some output to dib-lint
Add some output to dib-lint

It's hard to tell if dib-lint is working as it outputs nothing.  Add
some minimal output strings at some key points.

Change-Id: Id11cc9ecb8d5215d6fc8d8ef3584bfeeba53ff13

openstack/diskimage-builder,switch-ch/diskimage-builder,zioproto/diskimage-builder,openstack/diskimage-builder,switch-ch/diskimage-builder,zioproto/diskimage-builder