Never skip the performance tests.

The previous commit had the effect that they were run by default,
and only were skipped when the env variable was zero.
But that does not make much sense.

Also, even with a high test verbosity level (`bin/test -vvvvvv`),
sometimes the skip reason was shown and sometimes not.
The length of the reason seemed to matter at some point, but I could not get a grip on that.

plone/app/redirector/tests/test_performance.py

@@ -10,7 +10,7 @@
 env_name = 'PLONE_APP_REDIRECTOR_PERFORMANCE_NUMBER'
 if env_name in os.environ:
     # This could fail with a ValueError, but that seems a fine error message.
-    NUMBER = int(os.getenv(env_name))
+    NUMBER = max(int(os.getenv(env_name)), 1)
     VERBOSE = True
 else:
     # No environment variable set.
@@ -46,16 +46,9 @@ def timeit(self, message, limit=0):
                 '{0}: {1:.2f} seconds (max {2})'.format(message, total, limit)
             )
 
-    @unittest.skipIf(NUMBER <= 0, '{0} env variable not set'.format(env_name))
     def test_storage_performance(self):
         """Test the performance of some of the code.
 
-        This is skipped by default, unless you set an environment variable.
-        If you don't set this, or set this to zero or less, you will see
-        a skip reason when you run the tests with enough verbosity:
-
-            $ bin/test -s plone.app.redirector -m test_performance -vvv
-
         Sample run with one million inserts:
 
             $ PLONE_APP_REDIRECTOR_PERFORMANCE_NUMBER=1000000 \