[Java] Fix loading driver resources issue. (#3046)

## What do these changes do?
Fix the issue how we load driver resources by a specified path.
Also this addressed the comments from the related PR [3044](https://github.com/ray-project/ray/pull/3044).

## Related PRs:
 [#3044](https://github.com/ray-project/ray/pull/3044) and [#3001](https://github.com/ray-project/ray/pull/3001).

java/runtime/src/main/resources/ray.default.conf

@@ -25,15 +25,16 @@ ray {
   // Available resources on this node, for example "CPU:4,GPU:0".
   resources: ""
 
-    // Configuration items about driver.
-    driver {
-      // If worker.mode is DRIVER, specify the driver id.
-      // If not provided, a random id will be used.
-      id: ""
-      // If worker.mode is WORKER, it means that worker will load
-      // the resources from this path to execute tasks.
-      resource-path: /tmp/ray/driver/resource
-    }
+  // Configuration items about driver.
+  driver {
+    // If worker.mode is DRIVER, specify the driver id.
+    // If not provided, a random id will be used.
+    id: ""
+    // If this config is set, worker will use different paths to loadresources when
+    // executing tasks from different drivers. E.g. if it's set to '/tm/driver_resources',
+    // the path for driver 123 will be '/tmp/driver_resources/123'.
+    resource-path: ""
+  }
 
   // Root dir of log files.
   log-dir: /tmp/ray/logs