selftest: fix test_unsupported_subcommand test case

Fixed failure of test_unsupported_subcommand caused by
switching to argparser by checking that parser returns
non-zero return code.

[YOCTO #9636]

(From OE-Core rev: 581db38a280bf4cb03faf568cefd8d97383b5417)

Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/lib/oeqa/selftest/wic.py

@@ -159,8 +159,7 @@ class Wic(oeSelfTest):
     @testcase(1213)
     def test_unsupported_subcommand(self):
         """Test unsupported subcommand"""
-        self.assertEqual(1, runCmd('wic unsupported',
-                                   ignore_status=True).status)
+        self.assertNotEqual(0, runCmd('wic unsupported', ignore_status=True).status)
 
     @testcase(1214)
     def test_no_command(self):