Generation of git_commit_hash.py can fail

[Prof Garth Wells]

Generating git_commit_hash.py (which is done via setup.py) can fail when pip does its work in a tmp directory. The file git_commit_hash.py get generated in the wrong place.

To reproduce, follow exactly the pipelines file, but don't do an editable install (remove the e flag). Tested against Python 2/

[Jan Blechta]

You have to cd out of the repo dir. Otherwise you are trying to import from the repo directory where the generated file indeed is not present unless you do editable install.