recreate DB command

Drush, by default, will try to make a GRANT for each DB it creates:
http://drupalcontrib.org/api/drupal/contributions%21drush%21commands%21sql%21sql.drush.inc/function/drush_sql_build_createdb_sql/7

We dont necessarily want that; for a PR system with a wildcard grant (`GRANT ALL ON drupal_site_pr_%.*....`) we do not need the extra grants (something else to drop later).

This provides a simple "drop and create" dush command.