Python 3.5 Incompatibility

Context

Currently BuildGrid supports python 3.5 as a minimum. Currently some things in CAS break under 3.5. It should be worth noting that Debian-stable currently has python-3.5.

Task Description

* Decide the minimum python version which should be supported We will support 3.5

* If it is 3.5, resolve the following: Revolved

request.resource_name += f"blobs/{HASH(data_to_read).hexdigest()}/{len(data_to_read)}"

AttributeError: 'PosixPath' object has no attribute 'rfind'

Acceptance Criteria

If python3.5 is to be supported, we will need an image to reflect this such as debian-stable.