Can't execute multiple tests in parallel

[DanCardin]

Is your feature request related to a problem? Please describe.
pytest -n 4

E       sqlalchemy.exc.IntegrityError: (psycopg2.errors.UniqueViolation) duplicate key value violates unique constraint "pg_database_datname_index"
E       DETAIL:  Key (datname)=(pytest_mock_resource_db_386) already exists.
E        [SQL: 'CREATE DATABASE "pytest_mock_resource_db_386"'] (Background on this error at: http://sqlalche.me/e/gkpj)

Describe the solution you'd like
Starting here:
https://github.com/schireson/schireson-pytest-mock-resources/blob/master/src/pytest_mock_resources/fixture/database/relational/postgresql.py#L110

we shouldn't be setting the isolation level like that, firstly. but lastly the way that it's allocating the database names means we can't execute tests in parallel.

This is really unfortunate because otherwise the design seems really amenable to parallel use. This is a hard blocker to use in apis like flight-manager which would be really nice!