Add iscsictl(8) and iscsid(8) to rescue(8). The point is to make it
easier to build md_root images from rescue(8), to use with iSCSI boot.

The change increases the size of rescue by 62kB, from 8728kB to 8790kB.

Reviewed by: bapt@
MFC after: 1 month
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D3865