[SPARK-8379] [SQL] avoid speculative tasks write to the same file

The issue link [SPARK-8379](https://issues.apache.org/jira/browse/SPARK-8379)
Currently,when we insert data to the dynamic partition with speculative tasks we will get the Exception
```
org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.hdfs.server.namenode.LeaseExpiredException):
Lease mismatch on /tmp/hive-jeanlyn/hive_2015-06-15_15-20-44_734_8801220787219172413-1/-ext-10000/ds=2015-06-15/type=2/part-00301.lzo
owned by DFSClient_attempt_201506031520_0011_m_000189_0_-1513487243_53
but is accessed by DFSClient_attempt_201506031520_0011_m_000042_0_-1275047721_57
```
This pr try to write the data to temporary dir when using dynamic parition  avoid the speculative tasks writing the same file

Author: jeanlyn <jeanlyn92@gmail.com>

Closes #6833 from jeanlyn/speculation and squashes the following commits:

64bbfab [jeanlyn] use FileOutputFormat.getTaskOutputPath to get the path
8860af0 [jeanlyn] remove the never using code
e19a3bd [jeanlyn] avoid speculative tasks write same file