Reinitializes (copies python, etc binaries) into the venv when
dropping a new venv into place. This is needed because the Python
binary packaged with the venv may not match the Python running on
the host it is being installed to. (ie. in the case of a Xenial
repo container and a Trusty target host.)
Change-Id: Iec9b1be576a7e6e335deab6b199ff700e200f8e0
Partial-Bug: #1637509