[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