Fix for "cheets_CTS_N: disable max_retry on betty".

This fix the error "Unhandled TypeError: _get_release_channel()
takes exactly 2 arguments (1 given)".

BUG=chromium:750374
BUG=b:67331384
TEST=test_that cheets_CTS_N.CtsUsbTests

Change-Id: Ibccf5894a22fb918514cd1fce7be3c96f69b5ca6
Reviewed-on: https://chromium-review.googlesource.com/696745
Tested-by: Kazuhiro Inaba <kinaba@chromium.org>
Reviewed-by: Po-Hsien Wang <pwang@chromium.org>
Commit-Queue: Kazuhiro Inaba <kinaba@chromium.org>
Trybot-Ready: Kazuhiro Inaba <kinaba@chromium.org>
diff --git a/server/cros/tradefed_test.py b/server/cros/tradefed_test.py
index 4759ecf..2f4de21 100644
--- a/server/cros/tradefed_test.py
+++ b/server/cros/tradefed_test.py
@@ -982,7 +982,7 @@
         board_retry = self._get_board_retry(host)
         if board_retry is not None:
             return board_retry
-        channel_retry = self._get_channel_retry()
+        channel_retry = self._get_channel_retry(host)
         return channel_retry
 
     def _get_board_retry(self, host):
@@ -996,9 +996,9 @@
         logging.debug('No board retry specified for board: %s', board)
         return None
 
-    def _get_channel_retry(self):
+    def _get_channel_retry(self, host):
         """Returns the maximum number of retries for DUT image channel."""
-        channel = self._get_release_channel()
+        channel = self._get_release_channel(host)
         if channel in self._CHANNEL_RETRY:
             return self._CHANNEL_RETRY[channel]
         retry = self._CHANNEL_RETRY['dev']