[SPARK-2366] [SQL] Add column pruning for the right side of LeftSemi join.

The right side of `LeftSemi` join needs columns only used in join condition.

Author: Takuya UESHIN <ueshin@happy-camper.st>

Closes #1301 from ueshin/issues/SPARK-2366 and squashes the following commits:

7677a39 [Takuya UESHIN] Update comments.
786d3a0 [Takuya UESHIN] Rename method name.
e0957b1 [Takuya UESHIN] Add column pruning for the right side of LeftSemi join.

(cherry picked from commit 3da8df939ec63064692ba64d9188aeea908b305c)
Signed-off-by: Michael Armbrust <michael@databricks.com>