Set default locale

Neutron tempest plugin (common/ssh.py) gets locale for
execute scripts on remote machines, so set it to default
value to avoid an empty one.

Closes-Bug: PRODX-5583
Change-Id: If1b558c1fe85137716c0836b7049274affeef2c4

Dockerfile

@@ -2,6 +2,7 @@ ARG FROM=ubuntu:jammy
 FROM ${FROM}
 
 ENV PATH=/var/lib/openstack/bin:$PATH
+ENV LANG=C.UTF-8
 ARG PROJECT
 ARG WHEELS=loci/requirements:master-ubuntu_jammy
 ARG PROJECT_REPO=https://opendev.org/openstack/${PROJECT}