[SPARK-17732][SQL] ALTER TABLE DROP PARTITION should support comparators

[dongjoon-hyun]

What changes were proposed in this pull request?

This PR aims to support comparators, e.g. '<', '<=', '>', '>=', again in Apache Spark 2.0 for backward compatibility.

Spark 1.6

scala> sql("CREATE TABLE sales(id INT) PARTITIONED BY (country STRING, quarter STRING)")
res0: org.apache.spark.sql.DataFrame= [result: string]
scala> sql("ALTER TABLE sales DROP PARTITION (country < 'KR')")
res1: org.apache.spark.sql.DataFrame= [result: string]

Spark 2.0

scala> sql("CREATE TABLE sales(id INT) PARTITIONED BY (country STRING, quarter STRING)")
res0: org.apache.spark.sql.DataFrame= []
scala> sql("ALTER TABLE sales DROP PARTITION (country < 'KR')")
org.apache.spark.sql.catalyst.parser.ParseException:
mismatched input '<' expecting {')', ','}(line 1, pos 42)

After this PR, it's supported.

How was this patch tested?

Pass the Jenkins test with a newly added testcase.