virtualenv-tools has a bug which gets triggered in gates: it can't
change the shebang of a virtualenv python bin/ files if they
were generated with a virtualenv script whose shebang ends with
python2 instead of python.
Because we can't modify virtualenv-tools, we use shell scripts
instead.
Change-Id: I068bef7dcf354349a576ddf3dd3438f6489ffc4a
Partial-Bug: #1741634