civicrm-sql-* drush commands should function without a populated database

drush civicrm-sql-conf and civicrm-sql-cli error out if CIVICRM_DSN points to an empty database. The equivalent Drupal commands use drush bootstrap phases to initialize the DB connection, and stop there, not trying to do anything else, like loading the variables table from the DB. This will allow these commands to be more useful for maintenance, like loading an existing DB into a new installation.