usr_sbin/grml-setlang: Fix a couple of shellcheck warnings

usr_sbin/grml-setlang: Fix a couple of shellcheck warnings

- SC2086: Double quote to prevent globbing and word splitting.
- SC2034: CMDLINE appears unused. Verify use (or export if used externally).
- Ignore SC1091: Not following: /etc/grml/script-functions was not specified as input (see shellcheck -x).
- Ignore SC1091: Not following: /etc/grml/lsb-functions was not specified as input (see shellcheck -x).
- Ignore SC1117: Backslash is literal in "\#". Prefer explicit escaping: "\\#".
- Ignore SC1091: Not following: /etc/environment was not specified as input (see shellcheck -x).
- Ignore SC1091: Not following: /etc/default/locale was not specified as input (see shellcheck -x).
- Ignore SC1010: Use semicolon or linefeed before 'fi' (or quote to make it literal).
- SC2086: Double quote to prevent globbing and word splitting.
- Ignore SC1090: Can't follow non-constant source. Use a directive to specify location.
- SC2086: Double quote to prevent globbing and word splitting.