[SPARK-16503] SparkSession should provide Spark version

## What changes were proposed in this pull request?

This patch enables SparkSession to provide spark version.

## How was this patch tested?

Manual test:

```
scala> sc.version
res0: String = 2.1.0-SNAPSHOT

scala> spark.version
res1: String = 2.1.0-SNAPSHOT
```

```
>>> sc.version
u'2.1.0-SNAPSHOT'
>>> spark.version
u'2.1.0-SNAPSHOT'
```

Author: Liwei Lin <lwlin7@gmail.com>

Closes #14165 from lw-lin/add-version.