update_verifier: raise priority and ioprio and start with exec_start

Raise the priority and ioprio of update_verifier and launch with
exec_start.  This saves ~100ms of time before `class_start main` is executed.

Bug: 36511808
Bug: 36102163
Test: Boot bullhead
Test: Verify boottime decrease on sailfish
Change-Id: I944a6c0d4368ead5b99171f49142da2523ed1bdd
(cherry picked from commit 545317f4fb)

update_verifier/Android.mk

@@ -32,6 +32,8 @@ LOCAL_SHARED_LIBRARIES := \
 LOCAL_CFLAGS := -Werror
 LOCAL_C_INCLUDES += $(LOCAL_PATH)/..
 
+LOCAL_INIT_RC := update_verifier.rc
+
 ifeq ($(PRODUCTS.$(INTERNAL_PRODUCT).PRODUCT_SUPPORTS_VERITY),true)
     LOCAL_CFLAGS += -DPRODUCT_SUPPORTS_VERITY=1
 endif

update_verifier/update_verifier.rc

@@ -0,0 +1,11 @@
+service update_verifier_nonencrypted /system/bin/update_verifier nonencrypted
+    user root
+    class cache
+    priority -20
+    ioprio rt 1
+
+service update_verifier /system/bin/update_verifier ${vold.decrypt}
+    user root
+    class cache
+    priority -20
+    ioprio rt 1