Improve image processing on start command

* Added DuplicateException to properly handle case when
  same image already exists in glance;
* Implemented image cache to handle cached image files;
* Got rid of Registry as it is really needed;
* Other refactoring and clean-ups.

Change-Id: I512a6ecc104d4a5f23d52f4ad9ba1e80b33065cc
Closes-Bug: #1305786