Handle retry last_results/last_failure better

Provide properties on the atom/retry detail object to
allow access to last results instead of performing
the same type specific operation via storage allow
the object itself to provide the last result or last
failure instead.

Handle the resultant fetching failures correctly in
storage.py (instead of reraising index errors).

Change-Id: If33ff64d6173aba59d574d5997d07d91a36ec17e
Decrease extraneous logging

This log statement isn't very useful, and is a very active logging
statement used when no backend is provided, to avoid spewing to much
useless information into logs just remove it.

Fixes bug 1295880

Change-Id: I981185909f28bb20f96d56cb01cf5e1122f8d0a9
Merge "Handle retry last_results/last_failure better"
Merge "Decrease extraneous logging"