[SPARK-3225]Typo in script

use_conf_dir => user_conf_dir in load-spark-env.sh.

Author: WangTao <barneystinson@aliyun.com>

Closes #1926 from WangTaoTheTonic/TypoInScript and squashes the following commits:

0c104ad [WangTao] Typo in script

bin/load-spark-env.sh

@@ -27,12 +27,12 @@ if [ -z "$SPARK_ENV_LOADED" ]; then
   # Returns the parent of the directory this script lives in.
   parent_dir="$(cd `dirname $0`/..; pwd)"
 
-  use_conf_dir=${SPARK_CONF_DIR:-"$parent_dir/conf"}
+  user_conf_dir=${SPARK_CONF_DIR:-"$parent_dir/conf"}
 
-  if [ -f "${use_conf_dir}/spark-env.sh" ]; then
+  if [ -f "${user_conf_dir}/spark-env.sh" ]; then
     # Promote all variable declarations to environment (exported) variables
     set -a
-    . "${use_conf_dir}/spark-env.sh"
+    . "${user_conf_dir}/spark-env.sh"
     set +a
   fi
 fi