[WIP][CARBONDATA-3277] Support to show subquery for datamap

[kevinjmh]

What's in this PR:
support show query statement which was used to create preaggregate/mv datamap

Example output from testcase:

+-----------+------------+--------------------------+------------------+------------------------------------------+
|DataMapName|ClassName   |Associated Table          |DataMap Properties|Subquery                                  |
+-----------+------------+--------------------------+------------------+------------------------------------------+
|preagg1    |preaggregate|default.preaggmain_preagg1|                  |select a,sum(b) from PreAggMain group by a|
+-----------+------------+--------------------------+------------------+------------------------------------------+


+-----------+---------+----------------------+----------------------+---------------------------------------------+
|DataMapName|ClassName|Associated Table      |DataMap Properties    |Subquery                                     |
+-----------+---------+----------------------+----------------------+---------------------------------------------+
|datamap1   |mv       |default.datamap1_table|'full_refresh'='false'| select empname, designation from fact_table1|
+-----------+---------+----------------------+----------------------+---------------------------------------------+

+-----------+----------+---------------------------------+---------------------------------------------+-------------------------------------------------------------+
|DataMapName|ClassName |Associated Table                 |DataMap Properties                           |Subquery                                                     |
+-----------+----------+---------------------------------+---------------------------------------------+-------------------------------------------------------------+
|agg0_hour  |timeSeries|default.datamapshowtest_agg0_hour|'event_time'='mytime', 'hour_granularity'='1'|SELECT mytime, SUM(age) FROM datamapshowtest  GROUP BY mytime|
+-----------+----------+---------------------------------+---------------------------------------------+-------------------------------------------------------------+

How about add command? @2019.9.29

  protected lazy val descDataMap: Parser[LogicalPlan] =
    DESCRIBE ~> DATAMAP ~> ident <~ opt(";") ^^ {
      case dmname => CarbonDataMapShowCommand(None)
    }

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[CarbonDataQA]

Build Success with Spark 2.1.0, Please check CI http://136.243.101.176:8080/job/ApacheCarbonPRBuilder2.1/2477/

[CarbonDataQA]

Build Failed with Spark 2.3.2, Please check CI http://136.243.101.176:8080/job/carbondataprbuilder2.3/10735/

[CarbonDataQA]

Build Failed with Spark 2.2.1, Please check CI http://95.216.28.178:8080/job/ApacheCarbonPRBuilder1/2705/

[CarbonDataQA]

Build Success with Spark 2.1.0, Please check CI http://136.243.101.176:8080/job/ApacheCarbonPRBuilder2.1/2485/

[CarbonDataQA]

Build Success with Spark 2.3.2, Please check CI http://136.243.101.176:8080/job/carbondataprbuilder2.3/10743/

[CarbonDataQA]

Build Success with Spark 2.2.1, Please check CI http://95.216.28.178:8080/job/ApacheCarbonPRBuilder1/2712/

[CarbonDataQA]

Build Success with Spark 2.1.0, Please check CI http://136.243.101.176:8080/job/ApacheCarbonPRBuilder2.1/2541/

[CarbonDataQA]

Build Success with Spark 2.3.2, Please check CI http://136.243.101.176:8080/job/carbondataprbuilder2.3/10800/

[CarbonDataQA]

Build Success with Spark 2.2.1, Please check CI http://95.216.28.178:8080/job/ApacheCarbonPRBuilder1/2770/

[CarbonDataQA]

Build Success with Spark 2.1.0, Please check CI http://136.243.101.176:8080/job/ApacheCarbonPRBuilder2.1/2568/

[CarbonDataQA]

Build Success with Spark 2.3.2, Please check CI http://136.243.101.176:8080/job/carbondataprbuilder2.3/10827/

[CarbonDataQA]

Build Success with Spark 2.2.1, Please check CI http://95.216.28.178:8080/job/ApacheCarbonPRBuilder1/2798/

[kevinjmh]

When Subquery is too long, it will affect user experience for having a glance of all datamaps.

[qiuchenjian]

When Subquery is too long, it will affect user experience for having a glance of all datamaps.

@kevinjmh
Can you show the subquery multiply line and it has max character limit or use parameter to decide to whether show it

[qiuchenjian]

@kevinjmh
If this pr is finished in the future, please update the doc