[SPARK-4695][SQL] Get result using executeCollect

Using ```executeCollect``` to collect the result, because executeCollect is a custom implementation of collect in spark sql which better than rdd's collect

Author: wangfei <wangfei1@huawei.com>

Closes #3547 from scwf/executeCollect and squashes the following commits:

a5ab68e [wangfei] Revert "adding debug info"
a60d680 [wangfei] fix test failure
0db7ce8 [wangfei] adding debug info
184c594 [wangfei] using executeCollect instead collect

(cherry picked from commit 3ae0cda83c5106136e90d59c20e61db345a5085f)
Signed-off-by: Michael Armbrust <michael@databricks.com>