make it possible to change feedback plugin wait intervals
* only in debug builds
* and force the feedback report to be ignored
update the test to use this feature
2. dialog plugin now always returns mysql->password if non-empty and the first question is of password type
3. split get_tty_password into get_tty_password_buff and strdup.
4. dialog plugin now uses get_tty_password by default
5. dialog.test
6. moved small tests of individual plugins into a dedicated suite