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: Ic6c0efff4d9ac4b7616f558796cd211a04768a4c
Partial-Bug: #1637509