[SPARK-4504][Examples] fix run-example failure if multiple example jars present

Fix run-examples script error during multiple jars.
Modified to support failing fast similar to assembly.jar

Author: Venkata Ramana G <ramana.gollamudi@huawei.com>
For instance, `compute-classpath` uses

```bash
  jars_list=$(ls "$assembly_folder" | grep "spark-assembly.*hadoop.*.jar$")
```

for this; we should match this style rather than introducing a new one using backticks, `ls - t`, etc.