Recover from PRE_SKIP #2966

Make sure we write out events

This is for recovery in DAGman.  If we need to enter recovery mode, then
we need to have the events in the DAG so that recovery can proceed.

Introduce the STATUS_PRESKIP Job state, and use that in appropriate
places.

Don't increment the number of submitted jobs if we are in a PRESKIP
node.

Add some logic to Status state transitions in DAGMan jobs.

Correctly read the PreSkipEvent from the UserLog.

Set a node to PRESKIP Status upon reading the event.

Do not increment the submit counter if we are a PRESKIP job.

PRESKIP job should look like a NOOP

Write a test

Terminate a job, and include a Node with only a Pre Script. This touches
a different code path than nodes with a post script.

Include a version history comment