MySQL isolation level check does not work for JNDI datasources

The method Confluence is currently using for connecting to the database during bootstrap checks only works for C3P0 based connection settings. These settings are only set for direct JDBC connections, and are not available for JNDI datasource connections. Confluence needs to verify the connection settings by using whatever ConnectionProvider is appropriate (e.g. as determined by Hibernate's ConnectionProviderFactory), rather than just choosing one at random.

By failing to open connections in with the correct provider, Confluence will refuse to start for any customer using MySQL via a JNDI datasource, making this a blocker for any affected customer.