Add update_verifier for A/B OTA update.

update_verifier checks the integrity of the updated system and vendor
partitions on the first boot post an A/B OTA update. It marks the
current slot as having booted successfully if it passes the verification.

This CL doesn't perform any actual verification work which will be
addressed in follow-up CLs.

Bug: 26039641
Change-Id: Ia5504ed25b799b48b5886c2fc68073a360127f42
(cherry picked from commit 1171d3a12b13ca3f1d4301985cf068076e55ae26)
diff --git a/Android.mk b/Android.mk
index 22e7802..602a856 100644
--- a/Android.mk
+++ b/Android.mk
@@ -136,4 +136,5 @@
     $(LOCAL_PATH)/edify/Android.mk \
     $(LOCAL_PATH)/uncrypt/Android.mk \
     $(LOCAL_PATH)/updater/Android.mk \
+    $(LOCAL_PATH)/update_verifier/Android.mk \
     $(LOCAL_PATH)/applypatch/Android.mk