Don't return query from db API

The cell_update() method of the sqlalchemy db API returned a Query when
it really intended to return a Cell.  Fix this and tweak the db API test
so that it verifies that the result of this method is a Cell.

Change-Id: I7ab7ea19f00ac2e8c2c73afe8a14f331940b4580
Closes-bug: #1198796
Remove out of date list of jenkins jobs

The list of jobs in this doc file was out of date and most of the links
didn't work anymore.  Instead of trying to list out specifics which will
just get out of date again, include a generic pointer to where you can
find results (on code reviews).

Change-Id: Ief65281abae48bee6a679f76068e315227cf6991
Closes-bug: #1199577
Merge "Remove out of date list of jenkins jobs"
Merge "Don't return query from db API"
Reduce DB load caused by heal instance info cache

Load system metadata with instance fetches in the
_heal_instance_info_cache periodic task.  This will eliminate
DB queries to lazy load the system metadata in _get_instance_nw_info.

(lazy loading happens in the Instance object's obj_load_attr method)

bug 1223969

Change-Id: I835fc73ef3a92885cec174e1533db10e28752fe1