labs: force LC_ALL=C for ssh

Mac OS X exports LC_CTYPE=UTF-8 to our ssh environment which makes the
keystone install fail (results in a Python traceback complaining about
"unknown locale: UTF-8").

This patch uses LC_ALL=C to override all locale settings.

The previous, limited work-arounds for neutron are no longer needed and
removed.

Change-Id: Ic7a2f5547fc4bd5d512da5197e48366c83c21c24