remove unnecessary / redundant sparkTest() call

This was resulting in two SparkContexts being created during this test's
execution, which was leading to spurious socket-bind exceptions.
some style nits
make sparkTest()s find an unused UI port

this further avoids bind exceptions when tests are e.g. run in parallel.
un-parend some calls
Merge pull request #112 from hammerlab/test-bind-exceptions

Test bind exceptions