Set LANG and LC_ALL even if not present initially

One of the AWS instances that we set up had `/etc/default/locale` present, but only LANG was set (LC_ALL was not in the file at all). Since LC_ALL wasn't set, Salt [defaults to setting it to C](https://github.com/saltstack/salt/blob/develop/salt/modules/cmdmod.py#L357). This PR just creates our `/etc/default/locale` to be what we want it to be. (Sorry for not pushing this earlier @calebsmith, if this, in fact, does solve the problem you were having yesterday)