Allow usage of SQL connection parameters

By allowing the usage of connection parameters in the SQL connection string, we can pass useful parameters for i.e. Google Cloud SQL connection (using https://github.com/GoogleCloudPlatform/cloud-sql-jdbc-socket-factory for example), that would look like this :

jdbc:mysql://google:<PORT>/<DATABASE_NAME>?cloudSqlInstance=<INSTANCE_CONNECTION_NAME>&socketFactory=com.google.cloud.sql.mysql.SocketFactory

Currently it isn't possible to properly add connection parameters (except through an ugly hack in JDBCDriverConfig.constructProtocol()).

As far as I know, using a connection string with the aforementioned Cloud SQL JDBC Socket Factory is the only way I found to connect to Cloud SQL. Outside of using Cloud SQL, I believe this feature may be useful for some people that need to inject some parameters to their connection string to the database.