We already have old support for older python3.6 and bionic via this
method. Now that get-pip.py doesn't support python3.8 we do the same
thing for focal. It is unfortunate that they can't keep the script
broadly compatible but we already seem to have tooling to handle this so
take advantage of it.
Change-Id: Iba0838bc0757112905f7f1d5edfe1d3b395e470e