Bug #12984 mysqltest.test: different output from "exec NonExistsinfComamdn"

 - Common error handling regardless of --ps-protocol or not.


client/mysqltest.c:
  Merge normal_handle_error and run_query_stmt_handle_error to get consistent functionality and error messages regardless if --ps-protocol is used or not
  Call handle_error when error occured to check for expected error codes/states
  Call handle_no_error when no error ahs occured to check if an error was expected