labs: fix neutron locale

The neutron client fails with an "unsupported locale setting" message if
a locale is sent via ssh from the host computer to the node VM.

This changeset works around the problem by setting LC_ALL=C if the
problem is detected.

Change-Id: I9caa38c8fbe7d0d0e4025e4ba0c7fb537e1686de
Implements: blueprint openstack-training-labs