Keep verity state of the device invariant.

Test: manual
Change-Id: I19adb6305b582bc5b54535dbb232efe5886a2b82
diff --git a/utils/python/controllers/android_device.py b/utils/python/controllers/android_device.py
index dbef29a..3f096f5 100644
--- a/utils/python/controllers/android_device.py
+++ b/utils/python/controllers/android_device.py
@@ -405,6 +405,16 @@
         return "root" in id_str
 
     @property
+    def verityEnabled(self):
+        """True if verity is enabled for this device."""
+        try:
+            self.adb.shell('getprop | grep partition.system.verified').decode("utf-8")
+        except adb.AdbError:
+            # If verity is disabled, there is no property 'partition.system.verified'
+            return False
+        return True
+
+    @property
     def model(self):
         """The Android code name for the device."""
         # If device is in bootloader mode, get mode name from fastboot.