[SPARK-18527][SQL] Convert decimal array to double array double for Hive UDAFPercentile

[hvanhovell]

What changes were proposed in this pull request?

Hive UDAFPercentile takes a double or an array of doubles as its second argument. Spark typically passes a decimal or an array of decimals. This will causes a failure during function lookup for the percentile function.

We added a stop-gap measure in #13930 for doubles, by retrying the lookup with all decimal arguments casted to doubles. This PR extends this approach by adding the same logic for arrays of decimals.

Note that this is a temporary measure until #14136 is merged.

How was this patch tested?

Added a test to HiveUDFSuite

[SparkQA]

Test build #69243 has finished for PR 16034 at commit 0db2460.

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

[hvanhovell]

We have merged the percentile PR. So this does not need to be added to branch-2.1. branch-2.0 still has this problems, should we add it there? cc @rxin @yhuai

[rxin]

I'm ok not fixing this for branch-2.0.

[hvanhovell]

closing :)