Minor changes for runs of PCA on full datasets.

* quick and dirty hard-coded retry loop
* optionally saving output to durable location
* removed another cache operation for an RDD that is only used once
`val table = for ...` is now unnecessary, consider using the `for ... yield` as the last statement.
```
for (i <- 0 until pca.numRows)
       yield (reverse(i), array(i), array(i + pca.numRows))
```