Packaging cleanup: normalize print calls.

Namely: use default arguments instead of explicit empty string; use multiple
arguments instead of building strings.

Lib/packaging/util.py

@@ -1099,7 +1099,7 @@ def ask(message, options):
         response = input(message)
         response = response.strip().lower()
         if response not in options:
-            print('invalid response: %r' % response)
+            print('invalid response:', repr(response))
             print('choose one of', ', '.join(repr(o) for o in options))
         else:
             return response