tests: Require cmp

cmp is not by default installed on some containers
(unlike other tools e.g. cut, tr from coreutils or grep).

Also cmp implementation from busybox doesn't support -b, thus detect it.

Signed-off-by: Petr Vorel <pvorel@suse.cz>
Reviewed-by: Bruno Meneguele <bmeneg@redhat.com>(Fedora,CentOS 8(RHEL actually))
Signed-off-by: Mimi Zohar <zohar@linux.ibm.com>

tests/sign_verify.test

@@ -18,7 +18,14 @@
 cd "$(dirname "$0")" || exit 1
 PATH=../src:$PATH
 source ./functions.sh
-_require evmctl openssl xxd getfattr
+
+_require cmp evmctl getfattr openssl xxd
+
+if cmp -b 2>&1 | grep -q "invalid option"; then
+	echo "cmp does not support -b (cmp from busybox?) Use cmp from diffutils"
+	exit "$HARDFAIL"
+fi
+
 ./gen-keys.sh >/dev/null 2>&1
 
 trap _report_exit EXIT