On platforms such as CentOS 8 which are python3 first, "virtualenv"
and "pip" may not exist (removed to avoid any confusion over them
being v2 or v3 commands).
The referenced dib change exports new variables that should be correct
on all platforms for creating virtualenv's and pip installs.
(note will require DIB release to be active on builders)
Depends-On: https://review.opendev.org/684462
Change-Id: I3414fb9e503f94ff744b560eff9ec0f4afdbb50e
c5f807e699