[SPARK-4861][SQL] Refactory command in spark sql

Follow up for #3712.
This PR finally remove ```CommandStrategy``` and make all commands follow ```RunnableCommand``` so they can go with ```case r: RunnableCommand => ExecutedCommand(r) :: Nil```.

One exception is the ```DescribeCommand``` of hive, which is a special case and need to distinguish hive table and temporary table, so still keep ```HiveCommandStrategy``` here.

Author: scwf <wangfei1@huawei.com>

Closes #3948 from scwf/followup-SPARK-4861 and squashes the following commits:

6b48e64 [scwf] minor style fix
2c62e9d [scwf] fix for hive module
5a7a819 [scwf] Refactory command in spark sql