qi_install_python: avoid annoying warning

Change-Id: I2d4e92210cedb55ce43cec5988d4d1ff470e2d35
Reviewed-on: http://gerrit.aldebaran.lan/40316
Reviewed-by: dmerejkowsky <dmerejkowsky@aldebaran-robotics.com>
Tested-by: dmerejkowsky <dmerejkowsky@aldebaran-robotics.com>