SPARK-1619 Launch spark-shell with spark-submit

This simplifies the shell a bunch and passes all arguments through to spark-submit.

There is a tiny incompatibility from 0.9.1 which is that you can't put `-c` _or_ `--cores`, only `--cores`. However, spark-submit will give a good error message in this case, I don't think many people used this, and it's a trivial change for users.