Only install p4python on Python 2.7 or higher.
Review Request #105 — Created Nov. 15, 2022 and updated
There's no longer any version of p4python available that can be installed on Python 2.6. This change updates our `dev-requirements.txt` to only attempt to install on Python 2.7 or higher. Testing Done: Installed dependencies on Python 2.6 and 2.7 and ensured I only had the package on 2.7. Reviewed at https://reviews.reviewboard.org/r/9842/