[SPARK-10917] [SQL] improve performance of complex type in columnar cache

This PR improve the performance of complex types in columnar cache by using UnsafeProjection instead of KryoSerializer.

A simple benchmark show that this PR could improve the performance of scanning a cached table with complex columns by 15x (comparing to Spark 1.5).

Here is the code used to benchmark:

```
df = sc.range(1<<23).map(lambda i: Row(a=Row(b=i, c=str(i)), d=range(10), e=dict(zip(range(10), [str(i) for i in range(10)])))).toDF()
df.write.parquet("table")
```
```
df = sqlContext.read.parquet("table")
df.cache()
df.count()
t = time.time()
print df.select("*")._jdf.queryExecution().toRdd().count()
print time.time() - t
```

Author: Davies Liu <davies@databricks.com>

Closes #8971 from davies/complex.