Keep current rattail config, when launching overnight task

at least i think this makes the most sense..?

rattail/luigi/handler.py

@@ -184,7 +184,7 @@ class LuigiHandler(GenericHandler):
         appdir = self.config.appdir()
         env = {
             'PYTHONPATH': appdir,
-            'RATTAIL_CONFIG_FILES': os.path.join(appdir, 'silent.conf'),
+            'RATTAIL_CONFIG_FILES': os.pathsep.join(self.config.files_read),
         }
 
         # build our command, which will vary per caller request.  by
@@ -198,7 +198,6 @@ class LuigiHandler(GenericHandler):
             # rattail overnight <task>
             cmd = [
                 '{}/bin/rattail'.format(sys.prefix),
-                '--config', '{}/silent.conf'.format(appdir),
                 '--no-versioning',
                 'overnight', '-k', task['key'],
                 '--date={}'.format(date),
@@ -234,7 +233,6 @@ class LuigiHandler(GenericHandler):
             # rattail run-n-mail 'task command'
             cmd = [
                 os.path.join(sys.prefix, 'bin', 'rattail'),
-                '--config', os.path.join(appdir, 'silent.conf'),
                 '--no-versioning',
                 'run-n-mail',
                 '--keep-exit-code',
@@ -247,6 +245,7 @@ class LuigiHandler(GenericHandler):
                 cmd.append('--skip-if-empty')
 
         # log final command
+        log.debug("env is: %s", env)
         log.debug("launching command in subprocess: %s", cmd)
         if dry_run:
             log.debug("dry-run mode, so aborting")