improve check for createdb privileges during setup_db re: #4941

[mradamcox]

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Description of Change

Makes a better check for what type of postgres user Arches is provided with. The impetus for this change is that some hosted PG solutions (like AWS RDS) don't provide users with logins that are technically "superusers". However, the logins do have "CREATE DATABASE" ability, which is all that Arches actually needs when it tries to run the create/drop database operation.

Issues Solved

#4941

Checklist

• Unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Ticket Background

• Sponsored by: Legion GIS
• Designed by: @mradamcox

Further comments

[coveralls]

Coverage decreased (-0.009%) to 42.44% when pulling e75ccc3 on legiongis:4941_improve_pguser_createdb_chk_4.4.x into fef1c58 on archesproject:stable/4.4.x.