Temporarily patched in a hardcoded retry loop.

Instead we should make use of edb16e74dcc19c84a2c1268673edf608d1406f82 per issue #31.
Optionally save output of PCA to configured filesystem.

PCA results are written to stdout.  If an output path is passed in, results will also be written to the configured shared filesystem.

Also removed another cache operation for an RDD that is only used once.
Merge branch 'spark_pca_refactor'
Updates per feedback from @elmer-garduno.
Merge pull request #6 from deflaux/master

Minor changes for runs of PCA on full datasets.
Merge pull request #36 from elmer-garduno/master

Merge