modify cpu-freq test, insure last cpu avail
Add CpuFreq= header to scontrol show job output

Previous it just printed the value (e.g. "Low") without any
indication of what the information represented.
add job cpu-freq support

The --cpu-freq option from the sbatch/salloc command was
NOT logged as part of the RPC
NOT being stored in the slurmctld job record
NOT return as part of the job information once started (even if
    the data structure was populated, which was not the case)