Misleading error message when trying to CREATE DATABASE with insufficient permissions

When a user that does not have permission to create a database attempts to do so and fails, they get the following NOTICE message, which could lead to end user confusion:

```
citus=> create database foo;
NOTICE: Citus partially supports CREATE DATABASE for distributed databases
DETAIL: Citus does not propagate CREATE DATABASE command to workers
HINT: You can manually create a database and its extensions on workers.
ERROR: permission denied to create database
```

I'd suggest only adding the NOTICE message if the user has permissions to create the database.