Add /queued/ API

Returns a list of runs that have any queued jobs

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Use a much faster query for /runs/queued/

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Add unit tests for /runs/queued/

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Merge pull request #42 from ceph/queue-view

Add /queued/ API