[SPARK-2254] [SQL] ScalaRefection should mark primitive types as non-nullable.

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

Closes #1193 from ueshin/issues/SPARK-2254 and squashes the following commits:

cfd6088 [Takuya UESHIN] Modify ScalaRefection.schemaFor method to return nullability of Scala Type.
Merge branch 'master' into issues/SPARK-2287

Conflicts:
	sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/ScalaReflection.scala
	sql/catalyst/src/test/scala/org/apache/spark/sql/catalyst/ScalaReflectionSuite.scala