Normalize runtime threads in gantt chart

[effigies]

trafficstars

#3290 restored gantt chart functionality. The PR was generally delayed by a concern that the thread representation is misleading.

The proposed solution is:

if status_dict['runtime_threads'] != "N/A":
    status_dict['runtime_threads'] //= 100

I believe here:

https://github.com/nipy/nipype/blob/2e36f69a833529ee8b66c1c3fc43746db5a9fcea/nipype/utils/profiler.py#L174-L187

cc @shnizzedy