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: I8d0ac69bfca3757134086dbd0cb12be88473b6f8
Partial-Bug: #1637509