## What changes were proposed in this pull request?
`ExecutorClassLoader`'s `findClass` may fail to fetch a class due to transient exceptions. For example, when a task is interrupted, if `ExecutorClassLoader` is fetching a class, you may see `InterruptedException` or `IOException` wrapped by `ClassNotFoundException`, even if this class can be loaded. Then the result of `findClass` will be cached by JVM, and later when the same class is being loaded in the same executor, it will just throw NoClassDefFoundError even if the class can be loaded.
I found JVM only caches `LinkageError` and `ClassNotFoundException`. Hence in this PR, I changed ExecutorClassLoader to throw `RemoteClassLoadedError` if we cannot get a response from driver.
## How was this patch tested?
New unit tests.
Closes#24683 from zsxwing/SPARK-20547-fix.
Authored-by: Shixiong Zhu <zsxwing@gmail.com>
Signed-off-by: Shixiong Zhu <zsxwing@gmail.com>
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