Unable to use IAM credentials

[brosander]

Newer versions of the jdbc driver allow for use of IAM credentials instead of username/password. [1]

This is preferable to storing and passing around credentials.

It looks like the parameter validation in spark-redshift should be updated to reflect the new authentication method. [2]

[1] http://docs.aws.amazon.com/redshift/latest/mgmt/generating-iam-credentials-configure-jdbc-odbc.html
[2] https://github.com/databricks/spark-redshift/blob/master/src/main/scala/com/databricks/spark/redshift/Parameters.scala#L71

[brosander]

PR #374 opened, forking project due to note implying that this project isn't going to be supported going forward