ErrorLogFetch: fix a KeyError

Traceback:
File ".../troubleshoot/__init__.py", line 299, in _display
    result = question.display ()
File ".../troubleshoot/ErrorLogFetch.py", line 157, in display
    (answers['error_log_timestamp'], now))
KeyError: 'error_log_timestamp'

Author: jpopelka

troubleshoot/ErrorLogFetch.py

@@ -154,7 +154,7 @@ def journal_format (x):
             len (self.answers.get ('error_log', []))) == 0:
             cmd = ("su -c 'journalctl -u cups.service "
                    "--since=\"%s\" --until=\"%s\"' > troubleshoot-logs.txt" %
-                   (answers['error_log_timestamp'], now))
+                   (timestamp, now))
             self.entry.set_text (cmd)
             return True