[SPARK-5606][SQL] Support plus sign in HiveContext

Now spark version is only support ```SELECT -key FROM DECIMAL_UDF;``` in HiveContext.
This patch is used to support ```SELECT +key FROM DECIMAL_UDF;``` in HiveContext.

Author: q00251598 <qiyadong@huawei.com>

Closes #4378 from watermen/SPARK-5606 and squashes the following commits:

777f132 [q00251598] sql-case22
74dd368 [q00251598] sql-case22
1a67410 [q00251598] sql-case22
c5cd5bc [q00251598] sql-case22