base: use en_US.UTF-8 locale on all distros

C.UTF-8 is not supported in RHEL 7:

https://bugzilla.redhat.com/show_bug.cgi?id=1361965

Closes-bug: #1850035
Change-Id: I20dcb86e7e119b9f5ca44cd066fcb9cb84af1ce4

docker/base/Dockerfile.j2

@@ -4,7 +4,7 @@ LABEL maintainer="{{ maintainer }}" name="{{ image_name }}" build-date="{{ build
 {% block base_lang %}
 # NOTE(yoctozepto): use a UTF-8 (Unicode) locale like standard image installs do
 # fixes issues arising from ascii fallback usage
-ENV LANG C.UTF-8
+ENV LANG en_US.UTF-8
 {% endblock %}
 
 {# NOTE(SamYaple): Avoid uid/gid conflicts by creating each user/group up front. #}

releasenotes/notes/unicode-locale-018fe01eaccc556d.yaml

@@ -1,7 +1,7 @@
 ---
 upgrade:
   - |
-    ``C.UTF-8`` is set as the default locale (``LANG``) for images.
+    ``en_US.UTF-8`` is set as the default locale (``LANG``) for images.
     This affects both build- and run-time.
     Distributions supported by Kolla default to UTF-8 locale in
     installs so this change should provide a more expected experience.