Fix lazy coupling.

If slapos.libnetworkache is not available, setup environment in no-op way.

src/zc/buildout/buildout.py

@@ -336,7 +336,14 @@ class Buildout(UserDict.DictMixin):
 
         os.chdir(options['directory'])
 
-        if LIBNETWORKCACHE_ENABLED:
+        if not LIBNETWORKCACHE_ENABLED:
+            self._logger.warning('Networkache disabled, no '
+                'slapos.libnetworkache available.')
+            self.download_cache_url = None
+            self.download_dir_url = None
+            self.upload_cache_url = None
+            self.upload_dir_url = None
+        else:
             # support networkcache
             networkcache_section_name = options.get('networkcache-section')
             if networkcache_section_name:
@@ -360,7 +367,8 @@ class Buildout(UserDict.DictMixin):
                 options['__networkcache__upload-cache-url'] = self.upload_cache_url
                 options['__networkcache__upload-dir-url'] = self.upload_dir_url
             else:
-                self._logger.warning('Networkcache functionality not enabled.')
+                self._logger.warning('Networkcache functionality not enabled.'
+                    'In order to activate use networkcache-section.')
                 self.download_cache_url = None
                 self.download_dir_url = None
                 self.upload_cache_url = None