When we added this test I used ensure-pip in the ensure-twine role to
pull in the pip dependency. But we soon realised that ensure-twine
ran in a rootless context so couldn't install packages, and reverted
it with I2cf4224228860b8a2cddd360636bb8633967b07e.
However, this testing wasn't fixed up. Use ensure-pip in the test
playbook before we run the test, and add a note to ensure-twine that
it runs without privileges.
Change-Id: I6aef14b188dce8c4de774b09ddad718fec8fbf6c
e0a2b647a6