Cleanup for Sp_handler::show_create_sp

In order to implement packages easier, we'll do the following changes in Sp_handler::show_create_sp():

• Reverse the return value to the standard MariaDB notation: false on success, true on error
• Add a new parameter const DDL_options_st ddl_options and use it to process the OR REPLACE and IF NOT EXISTS clauses, instead of accessing thd->lex->create_info.