5686dbc45d
Adds USE_VENV to globally enable/disable use of virtual environments. ADDITIONAL_VENV_PACKAGES is used to manually add packages that do not appear in requirements.txt or test-requirements.txt to be installed into each venv. Database Python bindings are handled this way when a dataabse service is enabled. Change-Id: I9cf298b936fd10c95e2ce5f51aab0d49d4b7f37f