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: I9bb7aa62d5e191eb6de6f5295d77c57a08b2562d
Partial-Bug: #1637509