Sort MK_BSD_CPIO before MK_BSDINSTALL

Using sort(1) order makes verification of the sort easier.

Reviewed by: emaste, imp, netchild
Pull Request: https://github.com/freebsd/freebsd-src/pull/896

(cherry picked from commit 4ca5df80393e1f2bf6ac26af42fc7246acb59f71)