Improve logging when python-guestfs/libguestfs isn't working

Bumped from debug to warn level, as most often refers to
missing python-guestfs package or other libguestfs misconfiguration,
and the fallback path is usually not desired.

Closes-bug: 1240339
Change-Id: I5d90a3ea109e79fe17221c001f94d49d599048ba
Update devref setup docs for latest libvirt on ubuntu

Adds instructions on how to enable the ubuntu cloud-archive
and update to the latest libvirt-dev from the icehouse repo.

This is needed to run unit tests in Juno if you're still on
ubuntu precise.

Change-Id: I8c93afdd72256b2bdc487e1413bdd570a6ea59e8
docs - Fix docstring issues

fix identation, add line before block comment ends, remove
extra colon (:) to remove ERROR(s) and WARNING(s)

Change-Id: Iabb09867bf6068da35251f35f9f689a623420692
Merge "Improve logging when python-guestfs/libguestfs isn't working"
Merge "Update devref setup docs for latest libvirt on ubuntu"
Merge "docs - Fix docstring issues"