Remove "--python" flag from lf-activate-venv call in
capture-instance-metadata. This forces the system to use Python 2,
which is not available on newer systems, and is causing failures.
Change-Id: I456a1463885b6269b555edbd587c9cfc039c78da
Issue: RELENG-4192 Signed-off-by: Eric Ball <eball@linuxfoundation.org>