bsdgrep: add more tests for different binary flags

The existing 'binary' test in netbsd-tests/ does a basic check of the
default treatment for binary behavior, but not much more than that.
Given some opportunity for breakage recently that did not trigger any
failures, add some tests to cover the three different binary file
behaviors (a, -I, -U) and their --binary-files= equivalent values.

Submitted by: Kyle Evans <kevans91@ksu.edu>
Reviewed by: cem, ngie
Differential Revision: https://reviews.freebsd.org/D10620