Rename 'total elapsed time'

[nsheff]

### Pipeline completed. Epilogue
*        Elapsed time (this run):  0:00:17
*  Total elapsed time (all runs):  0:00:13
*         Peak memory (this run):  0.0197 GB
*        Pipeline completed time: 2019-10-24 15:42:13

This doesn't make sense, of course. the total time is only the sum of actual run processes.

maybe we just make that explicit:

### Pipeline completed. Epilogue
*        Elapsed time (this run):  0:00:17
*  Total process time (all runs):  0:00:13
*         Peak memory (this run):  0.0197 GB
*        Pipeline completed time: 2019-10-24 15:42:13

[nsheff]

So now we distinguish between 'elapsed time' and 'process time'.

[stolarczyk]

transferred to https://github.com/databio/pypiper/issues/170