autoscale Load Balancing issues

[brianhatchl]

When Hoot is run with multiple service/core instances (but a single db) behind a load balancer a few features have been identified that won't work.

• [x] File export: The export file gets written to the local file system of the node that received the export request, but there is no guarantee which node will received the download request, so some exports result in a 404 for the download file.

• [ ] Job cancel: A request can be made to cancel a job, which will kill the running hoot process, but this only works if the cancel request goes to the node running the job.

[maxgrossman]

ref #3170

[bobi7]

Note: add a poller that will see if a job is 'ready to cancel' and have it try to cancel the job