[SPARK-4433] fix a racing condition in zipWithIndex

Spark hangs with the following code:

~~~
sc.parallelize(1 to 10).zipWithIndex.repartition(10).count()
~~~

This is because ZippedWithIndexRDD triggers a job in getPartitions and it causes a deadlock in DAGScheduler.getPreferredLocs (synced). The fix is to compute `startIndices` during construction.

This should be applied to branch-1.0, branch-1.1, and branch-1.2.

pwendell

Author: Xiangrui Meng <meng@databricks.com>

Closes #3291 from mengxr/SPARK-4433 and squashes the following commits:

c284d9f [Xiangrui Meng] fix a racing condition in zipWithIndex