Fix config test dependency on $HOME.

system/t02_config/BadConfigTest_gold

@@ -1 +1 @@
-ERROR: error loading config file /Users/smira/.aptly.conf: invalid character 's' looking for beginning of object key string
+ERROR: error loading config file ${HOME}/.aptly.conf: invalid character 's' looking for beginning of object key string

system/t02_config/__init__.py

@@ -25,6 +25,8 @@ class BadConfigTest(BaseTest):
     runCmd = "aptly"
     expectedCode = 1
 
+    gold_processor = BaseTest.expand_environ
+
     def prepare(self):
         self.prepare_remove_all()