As far as building of OS images is nothing more than
just a stage of the whole OS installing procedure
it is sounds rational to implement this in terms
of fuel-agent. Besides, we already have plenty of utilities
which could be useful during building of images.
And some tasks are the same like pre-configuring
some files inside target OS.
Related-bug: #1433193
Implements: blueprint ibp-build-ubuntu-images
Change-Id: I3fadfb16e06e4ee16926da29b7b83ca005500698
9c5e3579bf