Make the default twine python installation use "python3". Use the
ensure-pip role before calling pip.
This role currently isn't tested; it is added with upload-pypi testing
in the follow-on Ie40ec32b3b2ffc4646301c6e145c527fe6a3bae2
Change-Id: I55ef79bf9c5af9e4d1da24ed654821277edb663b
Add twine_python so we can control the version of python used to
install twine.
Change-Id: I36ddbdf78f549ddc022cce86f3ada9631fb19c37
Signed-off-by: Doug Hellmann <doug@doughellmann.com>