teuthology/suite: log correct per-job description

Add 'description' to the items tracked in 'jobs_to_schedule'.
Make it a dict for somewhat clearer item extraction in the actual
scheduling loop.

Also fix an unrelated pep8 formatting error.

Fixes: #10283
Signed-off-by: Dan Mick <dan.mick@redhat.com>
Merge pull request #388 from ceph/wip-10283

teuthology/suite: log correct per-job description