[SPARK-6448] Make history server log parse exceptions

[ryan-williams]

This helped me to debug a parse error that was due to the event log format changing recently.

[SparkQA]

Test build #28949 has started for PR 5122 at commit c3742ae.

• This patch merges cleanly.

[srowen]

LGTM. The exception is otherwise completely swallowed, and this is supposed to be treated as an error.

[SparkQA]

Test build #28949 has finished for PR 5122 at commit c3742ae.

• This patch fails Scala style tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test FAILed.
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Test FAILed.

[ryan-williams]

oof, line length, fixing

[SparkQA]

Test build #28951 has started for PR 5122 at commit 5831656.

• This patch merges cleanly.

[SparkQA]

Test build #28951 has finished for PR 5122 at commit 5831656.

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

[AmplabJenkins]

Test PASSed.
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Test PASSed.