[SPARK-LLAP-62] Recover the change on default jar at SPARK-LLAP-59 (#63)
[SPARK-LLAP-62] Recover the change on default jar at SPARK-LLAP-59 (#63)

## What changes were proposed in this pull request?

`SPARK-LLAP-59` accidentally *reverts* the code of `SPARK-LLAP-53`. This broke `--packages` support in `spark-shell`. This PR recovers that.

```
// Make assembly as default artifact
...
```


## How was this patch tested?

Manual.

```
SPARK_MAJOR_VERSION=2 spark-shell --packages com.hortonworks.spark:spark-llap_2.11:1.0.7-2.1 --repositories ... --conf spark.sql.hive.llap=true
```

This closes #62 .
hortonworks-spark/spark-llap,hortonworks-spark/spark-llap,hortonworks-spark/spark-llap