[SPARK-12056][CORE] Create a TaskAttemptContext only after calling setConf.

TaskAttemptContext's constructor will clone the configuration instead of referencing it. Calling setConf after creating TaskAttemptContext makes any changes to the configuration made inside setConf unperceived by RecordReader instances.

As an example, Titan's InputFormat will change conf when calling setConf. They wrap their InputFormat around Cassandra's ColumnFamilyInputFormat, and append Cassandra's configuration. This change fixes the following error when using Titan's CassandraInputFormat with Spark:

*java.lang.RuntimeException: org.apache.thrift.protocol.TProtocolException: Required field 'keyspace' was not present! Struct: set_key space_args(keyspace:null)*

There's a discussion of this error here: https://groups.google.com/forum/#!topic/aureliusgraphs/4zpwyrYbGAE

Author: Anderson de Andrade <[email protected]>

Closes #10046 from adeandrade/newhadooprdd-fix.

(cherry picked from commit f434f36)
Signed-off-by: Marcelo Vanzin <[email protected]>

Author: Anderson de Andrade

core/src/main/scala/org/apache/spark/rdd/NewHadoopRDD.scala

@@ -138,14 +138,14 @@ class NewHadoopRDD[K, V](
       }
       inputMetrics.setBytesReadCallback(bytesReadCallback)
 
-      val attemptId = newTaskAttemptID(jobTrackerId, id, isMap = true, split.index, 0)
-      val hadoopAttemptContext = newTaskAttemptContext(conf, attemptId)
       val format = inputFormatClass.newInstance
       format match {
         case configurable: Configurable =>
           configurable.setConf(conf)
         case _ =>
       }
+      val attemptId = newTaskAttemptID(jobTrackerId, id, isMap = true, split.index, 0)
+      val hadoopAttemptContext = newTaskAttemptContext(conf, attemptId)
       private var reader = format.createRecordReader(
         split.serializableHadoopSplit.value, hadoopAttemptContext)
       reader.initialize(split.serializableHadoopSplit.value, hadoopAttemptContext)