Add support for using Slurm without accounting enabled

[Nicklas Nordborg]

The current implementation of the Slurm engine uses the sacct command to get information about finished jobs. However, this requires that accounting has been enabled in Slurm (it is disabled by default). It would be nice to have an alternative to use a status file similar to the "direct" engine. It should be relatively easy to let the current wrapper scripts create and update a status file. The drawback is that it will not catch problems that happens before the job is started, but this is probably rare and should only happen in case there is a misconfiguration on cluster.

This should be a configurable option for the <cluster> entry in opengrid-config.xml. The default should be to use accounting.