image-fuzzer: Use OSerror.strerror instead of tuple subscript

OSError can't be used like a tuple on Python 3, so change the
code to use `e.sterror` instead of `e[1]`.

Reported-by: John Snow <jsnow@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Message-id: 20191021214117.18091-1-ehabkost@redhat.com
Message-Id: <20191021214117.18091-1-ehabkost@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

tests/image-fuzzer/runner.py

@@ -159,7 +159,7 @@ class TestEnv(object):
             os.makedirs(self.current_dir)
         except OSError as e:
             print("Error: The working directory '%s' cannot be used. Reason: %s"\
-                % (self.work_dir, e[1]), file=sys.stderr)
+                % (self.work_dir, e.strerror), file=sys.stderr)
             raise TestException
         self.log = open(os.path.join(self.current_dir, "test.log"), "w")
         self.parent_log = open(run_log, "a")
@@ -246,7 +246,7 @@ class TestEnv(object):
             except OSError as e:
                 multilog("%sError: Start of '%s' failed. Reason: %s\n\n"
                          % (test_summary, os.path.basename(current_cmd[0]),
-                            e[1]),
+                            e.strerror),
                          sys.stderr, self.log, self.parent_log)
                 raise TestException