Grant / revoke in Redshift for groups

[AntoineAugusti]

Unfortunately, Redshift enforces the presence of the GROUP statement when dealing with a group. It is optional in PostgreSQL

• Redshift: http://docs.aws.amazon.com/redshift/latest/dg/r_GRANT.html
• PostgreSQL: https://www.postgresql.org/docs/9.1/static/sql-grant.html

This difference breaks grants in Redshift. It seems that we need to determine if a role is a user or a role and pass this info to the various methods.