Split new function out into a separte utility script and add a test for it. Can be used in future to organise re/commonly-used code

Signed-off-by: Adam Warner <me@adamwarner.co.uk>

advanced/Scripts/utils.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+# Pi-hole: A black hole for Internet advertisements
+# (c) 2017 Pi-hole, LLC (https://pi-hole.net)
+# Network-wide ad blocking via your own hardware.
+#
+# Script to hold utility functions for use in other scripts
+#
+# This file is copyright under the latest version of the EUPL.
+# Please see LICENSE file for your rights under this license.
+
+# Basic Housekeeping rules
+#  - Functions must be self contained
+#  - Functions must be added in alphabetical order
+#  - Functions must be documented
+#  - New functions must have a test added for them in test/test_any_utils.py
+
+#######################
+# Takes three arguments key, value, and file.
+# Checks the target file for the existence of the key
+#   - If it exists, it changes the value
+#   - If it does not exist, it adds the value
+#
+# Example usage:
+# addOrEditKeyValuePair "BLOCKING_ENABLED" "true" "/etc/pihole/setupVars.conf"
+#######################
+addOrEditKeyValPair() {
+  local key="${1}"
+  local value="${2}"
+  local file="${3}"
+  if grep -q "^${key}=" "${file}"; then
+    sed -i "/^${key}=/c\\${key}=${value}" "${file}"
+  else
+    echo "${key}=${value}" >> "${file}"
+  fi
+}