Added defaults_file to mysql_db

   - The defaults_file will be loaded if passed, otherwise, ~/.my.cnf would be loaded.  Any parameters
     passed will override the parameters found in the my.cnf file.  user, password, host, port and socket
     parameters will be read from the my.cnf.
   - If user not found, root will be used
   - If password not found, no password will be used.  It is no longer required.