Allow database creation for non-local databases

[icemac]

@sallner wrote at 2018-04-10:

For test setups on bitbucket pipelines with postgres as a service, we have a test system, where there is no createdb command available. Instead a connection to the postgres on localhost is possible.
I would like to have gocept.testdb to use this connection instead of CLI programs to create a database.
Inspiration may be found here: https://stackoverflow.com/a/8977109/8531885 http://sqlalchemy-utils.readthedocs.io/en/latest/database_helpers.html connection.execute('CREATE DATABASE test')