fix missing shlex import in error path

Regression in commit 002cd09. Since the
function we need isn't invisibly exposed via portage.*, we need to
distinctly import it. We did in most cases, but not here.

Caught by flake8's missing imports linter. Unfortunately, the overall
usefulness of flake8 here is effectively nil, because lazyimport means
*all* imports are "missing". It is too noisy to believe. But I actually
spotted this error, it's not a false positive, and we might as well fix
it immediately.

Fixes: 002cd09
Signed-off-by: Eli Schwartz <eschwartz@gentoo.org>
Closes: #1438
Signed-off-by: Mike Gilbert <floppym@gentoo.org>

Author: eli-schwartz

bin/install.py

@@ -4,6 +4,7 @@
 
 import argparse
 import os
+import shlex
 import stat
 import sys
 import subprocess