main/bind: depend on bind-tools
The install script needs to call rndc-confgen to generate a key which is required for reloading to work.
955e3791 (main/bind: add support for "reload", 2019-10-19) added support for reload, but that causes an issues when installing bind, because rndc-confgen is in the bind-tools subpackage, which is not available if you just install bind.
Fix this by having bind depend on bind-tools.