Handle slashes in Presto schemas for SQLAlchemy URL

When connecting a PrestoDB database to query a Apache Pulsar SQL worker, errors are occurring when working with a schema containing slashes.

The check from: https://github.com/dropbox/PyHive/blob/master/pyhive/sqlalchemy_presto.py#L106 is raising an exception whereas I expected the schema to contain the slash.

I believe the check should be removed or we need a way to escape the slashes:

- presto://localhost:8081/pulsar/public/default
- presto://localhost:8081/pulsar/public%2Fdefault

Example of integration can be found here: https://github.com/apache/incubator-superset/pull/7297