[CI] Hook cli-tests up to CI

Add cli-tests to `make test`. This adds a `python3` dependency to `make
test`, but not `make check`. We could make this dependency optional by
skipping the tests if `python3` is not present.

tests/cli-tests/basic/help.sh

@@ -1,4 +1,7 @@
-#!/bin/sh -e
+#!/bin/sh
+
+set -e
+
 println "+ zstd -h"
 zstd -h
 println "+ zstd -H"

tests/cli-tests/basic/version.sh

@@ -1,3 +1,6 @@
-#!/bin/sh -e
+#!/bin/sh
+
+set -e
+
 zstd -V
 zstd --version