Handle invalid options in arc_summary

If an invalid option is provided to arc_summary.py we handle any error
thrown from the getopt Python module and print the usage help message.

Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #6983

tests/zfs-tests/tests/functional/cli_user/misc/Makefile.am

@@ -46,4 +46,5 @@ dist_pkgdata_SCRIPTS = \
 	zpool_upgrade_001_neg.ksh \
 	arcstat_001_pos.ksh \
 	arc_summary_001_pos.ksh \
+	arc_summary_002_neg.ksh \
 	dbufstat_001_pos.ksh

tests/zfs-tests/tests/functional/cli_user/misc/arc_summary_002_neg.ksh

@@ -0,0 +1,38 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# The contents of this file are subject to the terms of the
+# Common Development and Distribution License (the "License").
+# You may not use this file except in compliance with the License.
+#
+# You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+# or http://www.opensolaris.org/os/licensing.
+# See the License for the specific language governing permissions
+# and limitations under the License.
+#
+# When distributing Covered Code, include this CDDL HEADER in each
+# file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+# If applicable, add the following below this CDDL HEADER, with the
+# fields enclosed by brackets "[]" replaced with your own identifying
+# information: Portions Copyright [yyyy] [name of copyright owner]
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2015 by Lawrence Livermore National Security, LLC.
+# All rights reserved.
+#
+
+. $STF_SUITE/include/libtest.shlib
+
+typeset args=("-x" "-r" "-5" "-p 7" "--err" "-@")
+
+log_assert "arc_summary.py generates an error code with invalid options"
+
+for arg in "${args[@]}"; do
+        log_mustnot eval "arc_summary.py $arg > /dev/null"
+done
+
+log_pass "arc_summary.py generates an error code with invalid options"