Bluetooth: Correct interface for log collection during BT tests

I had changed one part of the log collection API as part of the CL
review two months ago, but missed the change on the caller to match;
therefore, the log collection feature has been inactive. This change
fixes the interface.

BUG=b:173247857
TEST=Ran a test with a fake failure to ensure the log is caught properly

Change-Id: I3d39565384269efa296b3f3a93629e4372a12115
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/autotest/+/2577760
Tested-by: Daniel Winkler <danielwinkler@google.com>
Auto-Submit: Daniel Winkler <danielwinkler@google.com>
Reviewed-by: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
Commit-Queue: Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
diff --git a/server/cros/bluetooth/bluetooth_device.py b/server/cros/bluetooth/bluetooth_device.py
index be3fd03..a1aaa76 100644
--- a/server/cros/bluetooth/bluetooth_device.py
+++ b/server/cros/bluetooth/bluetooth_device.py
@@ -1087,8 +1087,12 @@
 
     @proxy_thread_safe
     def messages_stop(self):
-        """Stop messages monitoring."""
-        self._proxy.messages_stop()
+        """Stop messages monitoring.
+
+        @returns: True if logs were successfully gathered since logging started,
+                else False
+        """
+        return self._proxy.messages_stop()
 
     @proxy_thread_safe
     def messages_find(self, pattern_str):