Propagate ExecutionExceptions from the driver thread to the client

In AbstractSparkClient we have the following code:

       try {
          driverFuture.get();
        } catch (InterruptedException ie) {
          // Give up.
          LOG.warn("Interrupted before driver thread was finished.", ie);
        } catch (ExecutionException ee) {
          LOG.error("Driver thread failed", ee);
        }

If the driver Future throws an ExecutionException the error is simply logged, and a RuntimeException is thrown with the generic message "Error while waiting for Remote Spark Driver to connect back to HiveServer2."

We should propagate the ExecutionException to the client.