Implement an allocateNodes "auto"

In this issue I add to allocateNodes functionality by having an "auto" mode in which a number of glide-ins are submitted to USDF/S3DF-Slurm in response to detected "job pressure" / Idle jobs in the queue. This may involve using functions of glideinwms package for convenience.  The tool will emulate the  glideinwms frontend / factory in a very specific, simple context (USDF/S3DF-Slurm). As such the user does not have to specify a number N of glide-ins etc.  User input can be minimal (default setting like  100 maximum glide-ins, 16 cores per glide-in, etc might suffice.)  This mode could be investigated to run as part /sidecar of workflows themselves, but that is a followup issue.