SSP-2900 Dial back job queue scheduling task frequency

By default the job scheduler now fires every 15s rather than every 5s.

For job execution workflows which implement batched execution (which
is all of them), there is also now a 1s (hardcoded) sleep between each
batch so long running jobs don't completely monopolize computing
resources. And the batched workflow loop now checks for thread
interruption before each iteration. An interrupted job is set
back to a QUEUED state but its execution state is preserved. That
way it can be restarted after the interruption is dealt with. (This
requeue behavior already existed, we just weren't checking for thread
interruptions in the batching loop.)