[SPARK-5067][Core] Use '===' to compare well-defined case class

[zsxwing]

A simple fix would be adding assert(e1.appId == e2.appId) for SparkListenerApplicationStart. But actually we can use === for well-defined case class directly. Therefore, instead of fixing this issue, I use === to compare those well-defined case classes (all fields have implemented a correct equals method, such as primitive types)

[SparkQA]

Test build #25024 has started for PR 3886 at commit 0a51711.

• This patch merges cleanly.

[SparkQA]

Test build #25024 has finished for PR 3886 at commit 0a51711.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test PASSed.
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Test PASSed.

[rxin]

LGTM. Merging in master. Thanks!