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

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

- Ignore SC1091: Not following: /etc/grml/script-functions was not specified as input (see shellcheck -x).
- SC1117: Backslash is literal in "\n". Prefer explicit escaping: "\\n".
- SC1117: Backslash is literal in "\n". Prefer explicit escaping: "\\n".
- SC2086: Double quote to prevent globbing and word splitting.
- Ignore SC1117: Backslash is literal in "\(". Prefer explicit escaping: "\\(".
- Ignore SC1117: Backslash is literal in "\s". Prefer explicit escaping: "\\s".
- Ignore SC1117: Backslash is literal in "\)". Prefer explicit escaping: "\\)".
- Ignore SC1117: Backslash is literal in "\1". Prefer explicit escaping: "\\1".
- Ignore SC1117: Backslash is literal in "\(". Prefer explicit escaping: "\\(".
- Ignore SC1117: Backslash is literal in "\s". Prefer explicit escaping: "\\s".
- Ignore SC1117: Backslash is literal in "\)". Prefer explicit escaping: "\\)".
- Ignore SC1117: Backslash is literal in "\1". Prefer explicit escaping: "\\1".
- SC2046: Quote this to prevent word splitting.