redshift does not allow create superuser without password

[mtesch-um]

Attempting to create a user as superuser without setting a password gives this error from redshift at apply-time.

error creating user mysuperuser: pq: CREATEUSER and PASSWORD DISABLE are incompatible

It would be nicer to have an error on the plan phase.

[mtesch-um]

ps. fantastic work! thank you so much for creating and sharing this project!