AK2: introduce .prop files patching function

patch_prop:
- if matched name is not present, appends new prop entry to the end of the file
- if matched name is present, replaces the entry with the new value

tools/ak2-core.sh

@@ -302,5 +302,15 @@ patch_cmdline() {
   fi;
 }
 
+# patch_prop <prop file> <prop name> <new prop value>
+patch_prop() {
+  if [ -z "$(grep "^$2=" $1)" ]; then
+    echo -ne "\n$2=$3\n" >> $1;
+  else
+    line=`grep -n "^$2=" $1 | head -n1 | cut -d: -f1`;
+    sed -i "${line}s;.*;${2}=${3};" $1;
+  fi;
+}
+
 ## end methods