autotest: suppress logging for adb devices

When doing the adb devices command, the output will not be logged
to prevent logs from exploding.

BUG=chromium:722566
TEST=Tested locally to make sure log messages were suppresed.

Change-Id: I31b42b46ec8e36c44f62bb9387db8b8ac4a8d8fb
Reviewed-on: https://chromium-review.googlesource.com/522544
Tested-by: Benjamin Peake <bpeake@chromium.org>
Reviewed-by: Dan Shi <dshi@google.com>
Commit-Queue: Benjamin Peake <bpeake@chromium.org>
Trybot-Ready: Benjamin Peake <bpeake@chromium.org>
diff --git a/server/hosts/adb_host.py b/server/hosts/adb_host.py
index d70bd5d..0e764a8 100644
--- a/server/hosts/adb_host.py
+++ b/server/hosts/adb_host.py
@@ -298,6 +298,10 @@
 
         Refer to _device_run method for docstring for parameters.
         """
+        # Suppresses 'adb devices' from printing to the logs, which often
+        # causes large log files.
+        if command == "devices":
+            kwargs['verbose'] = False
         return self._device_run(ADB_CMD, command, **kwargs)