HPCC-8189 JobQueue updating dali too frequently

Both eclccserver and roxie were setting short timeouts on the call to
jobq.dequeue, in order to ensure they could close down cleanly and quickly.

However, this resulted in frequent writes to dali to update the queue
status (several per second), meaning dali would never do idle and the
inc file would grow unnecessarily large.

Use the async cancelAcceptConversation method means we can close down even
faster, and avoids the dali noise.

There is still a timeout every 900s (in a defualt configuration) on the
dfuserver monitor queue. That cannot be eliminated without more significant
refactoring.

Signed-off-by: Richard Chapman <rchapman@hpccsystems.com>