base/dracut-lib.sh: add trim()

trim() to remove leading and trailing whitespace

(cherry picked from commit ac422d577c)

modules.d/99base/dracut-lib.sh

@@ -51,6 +51,13 @@ str_ends() {
     [ "${1%*"$2"}" != "$1" ]
 }
 
+trim() {
+    local var="$*"
+    var="${var#"${var%%[![:space:]]*}"}"   # remove leading whitespace characters
+    var="${var%"${var##*[![:space:]]}"}"   # remove trailing whitespace characters
+    echo -n "$var"
+}
+
 if [ -z "$DRACUT_SYSTEMD" ]; then
 
     warn() {