Support preemptible containers on LSF
HPC systems can support low priority / preemptible jobs similar to cloud. One way is by having a separate "preemptible" queue.
Propose that, similar to GPU support, if a job is marked "preemptible", the Arvados configuration can supply a command line fragment that submits the job to a site-specific "preemptible" queue.
The dispatcher must also recognize when a job has been preempted and behave appropriately (e.g. not try to re-submit the job). I.e. when LSF preempts a job, it can be configured to suspend it with SIGSTOP and keep it in in memory to resume later. We don't want Arvados to think a suspended job has failed and try to cancel it.