Add pip 9.0.3 to conda environment to avoid numpy 1.9.3 error 
I obtain this error:
'No matching distribution found for numpy==1.9.3'.
See #20952 for more details. This change works for me. Closes #20952 .

- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry