Ticket #48934 - remove-ds.pl deletes an instance even if wrong prefix was specified
Description: remove-ds.pl skipped to check "slapd" part of "slapd-instance".
This patch adds the check and if it is not "slapd", it quits with the error
message. For example:
Error: Invalid instance name "bogus-test"
Reviewed by firstname.lastname@example.org (Thanks, Mark!!)