update_verifier: tweak priority of update_verifier for quick boot

Highest ioprio is 0 for CFQ and we should run update_verifier with that.
Tested on device and showing boottime decreased.

Bug: 36511808
Bug: 36102163
Test: Boot marlin
Change-Id: Iddd925951d976e21014b61e5590bcdae3cea8470
(cherry picked from commit a015cd1d7a3af5d9c06622e00be47fee52ba4b02)
diff --git a/update_verifier/update_verifier.rc b/update_verifier/update_verifier.rc
index fc8a64d..8b60c3f 100644
--- a/update_verifier/update_verifier.rc
+++ b/update_verifier/update_verifier.rc
@@ -2,10 +2,10 @@
     user root
     class cache
     priority -20
-    ioprio rt 1
+    ioprio rt 0
 
 service update_verifier /system/bin/update_verifier ${vold.decrypt}
     user root
     class cache
     priority -20
-    ioprio rt 1
\ No newline at end of file
+    ioprio rt 0