hexdump: tests: take into account byte order

Hexdump test was failling on big endian systems when testing decimal, octal
and hexa outputs as the tests were designed on a little endian system. This
revision adds the two distinct flavors of output expected and determines at
runtime which to compare against.

Submitted by: Renato Riolino <renato.riolino_eldorado.org.br>
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D23191