bad return code on 404

[yoshi314]

If i get a 404 on crl, plugin is expected to throw a critical, but it throws a warning because the temporary crl file is not on the disk and the os.remove(tmpcrl) fails.

So the exception to handle 404 gets overridden by exception due to attempting to delete a file that no longer exists.

A quick fix:

         urllib.request.urlretrieve(url, tmpcrl)
     except:
         print ("CRITICAL: CRL could not be retrieved: %s" % url)
-        os.remove(tmpcrl)
+        if os.path.exists(tmpcrl):
+            os.remove(tmpcrl)
         sys.exit(2)