[SPARK-10400] [SQL] Renames SQLConf.PARQUET_FOLLOW_PARQUET_FORMAT_SPEC (for branch-1.5)

[liancheng]

Same as #8566, but for branch-1.5.

[liancheng]

Would be nice to have this merged into branch-1.5 if we were having another RC.

[SparkQA]

Test build #41920 has finished for PR 8568 at commit e982c06.

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

[SparkQA]

Test build #42414 has finished for PR 8568 at commit 3789ac8.

• This patch fails to build.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #42545 has finished for PR 8568 at commit ab61a59.

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

[liancheng]

I'm closing this one. Probably not necessary to backport this one to branch-1.5.