[MOP] logfiles to contain .git commit ID

[mtbannister]

If the logfiles for the various steps of the pipeline wrote out the .git commit ID that they were currently running with, we would have a record of exactly what version of the pipeline was used to process a given set of data.

This is nice for reproducibility/error-tracking. And it would be something that we could put at appropriate points as a footnote in the OSSOS papers.