[SPARK-2135][SQL] Use planner for in-memory scans

Author: Michael Armbrust <michael@databricks.com>

Closes #1072 from marmbrus/cachedStars and squashes the following commits:

8757c8e [Michael Armbrust] Use planner for in-memory scans.

(cherry picked from commit 13f8cfdc04589b986554310965e83fe658085683)
Signed-off-by: Michael Armbrust <michael@databricks.com>