[Followup SPARK-8387][WEBUI] Update driver log URL to show only 4096 bytes

[carsonwang]

This is to follow up #6834 , update the driver log URL as well for consistency.

[srowen]

Do you need to update YarnClusterSuite too? looks like it expects start=0

[carsonwang]

Thanks for the reminder, @srowen ! The url in YarnClusterSuite is now updated.

[SparkQA]

Test build #35118 has finished for PR 6878 at commit a0004f4.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • case class CreateStruct(children: Seq[Expression]) extends Expression

[SparkQA]

Test build #35120 has finished for PR 6878 at commit 13be948.

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

[harishreedharan]

As long as -4096 works (I didn't test this), this LGTM.

[andrewor14]

LGTM, merging into master.