[SPARK-12395] [SQL] fix resulting columns of outer join

For API DataFrame.join(right, usingColumns, joinType), if the joinType is right_outer or full_outer, the resulting join columns could be wrong (will be null).

The order of columns had been changed to match that with MySQL and PostgreSQL [1].

This PR also fix the nullability of output for outer join.

[1] http://www.postgresql.org/docs/9.2/static/queries-table-expressions.html

Author: Davies Liu <davies@databricks.com>

Closes #10353 from davies/fix_join.