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
I'm almost certain this saveAsTextFile will output the tuples as (a,b,c), consider using something like:

```
resultRdd.map(tuple => s"${tuple._1}\t${tuple._2}\t${tuple._3}").saveAsTextFile(conf.outputPath() + "-pca.txt")
```

to make the results simpler to parse.