Extend device with sleep functionality

This changeset adds the ability to sleep on the device via a
device.sleep() method. This invokes sleep on the target device. This
is useful for situations where the passage of time on the target
device does not match that of the host, e.g., gem5.

This changeset also updates a number of workloads to use this new
sleep method.

wlauto/workloads/nenamark/__init__.py

@@ -16,7 +16,6 @@
 
 import os
 import re
-import time
 
 from wlauto import AndroidBenchmark, Parameter
 
@@ -50,9 +49,9 @@ class Nenamark(AndroidBenchmark):
     regex = re.compile('.*NenaMark2.*Score.*?([0-9\.]*)fps')
 
     def run(self, context):
-        time.sleep(5)  # wait for nenamark menu to show up
+        self.device.sleep(5)  # wait for nenamark menu to show up
         self.device.execute('input keyevent 23')
-        time.sleep(self.duration)
+        self.device.sleep(self.duration)
 
     def update_result(self, context):
         super(Nenamark, self).update_result(context)