allow CheckKey to request mounting /system

Also provide a default implementation of CheckKey that's reasonable
for many devices (those that have power and volume keys).

Change-Id: Icf6c7746ebd866152d402059dbd27fd16bd51ff8
diff --git a/Android.mk b/Android.mk
index 075fa2c..645a835 100644
--- a/Android.mk
+++ b/Android.mk
@@ -82,6 +82,7 @@
 LOCAL_MODULE := verifier_test
 LOCAL_FORCE_STATIC_EXECUTABLE := true
 LOCAL_MODULE_TAGS := tests
+LOCAL_CFLAGS += -DNO_RECOVERY_MOUNT
 LOCAL_SRC_FILES := \
     verifier_test.cpp \
     verifier.cpp \