Update from https://crrev.com/327068

build/android/host_heartbeat.py

Index: build/android/host_heartbeat.py
diff --git a/build/android/host_heartbeat.py b/build/android/host_heartbeat.py
index 429fca9ac1c96309e09e7dd04bbcc2401c4f74d0..6a7cdd1d8e6bdb96e1b29f0725fac5f82f811b15 100755
--- a/build/android/host_heartbeat.py
+++ b/build/android/host_heartbeat.py
@@ -12,7 +12,6 @@ This heart beat lets the devices know that they are connected to a host.
 import sys
 import time
 
-from pylib import android_commands
 from pylib.device import device_utils
 
 PULSE_PERIOD = 20
@@ -20,10 +19,10 @@ PULSE_PERIOD = 20
 def main():
   while True:
     try:
-      devices = android_commands.GetAttachedDevices()
-      for device_serial in devices:
-        device_utils.DeviceUtils(device_serial).RunShellCommand(
-            'touch /sdcard/host_heartbeat')
+      devices = device_utils.DeviceUtils.HealthyDevices()
+      for d in devices:
+        d.RunShellCommand(['touch', '/sdcard/host_heartbeat'],
+                          check_return=True)
     except:
       # Keep the heatbeat running bypassing all errors.
       pass