Use snapshot value sys.fuse_snapshot instead of persist.sys.fuse

This will allow us to receive values from server flags and store them in
persist.sys.fuse without risking flag consistency during a boot.

Test: manual - flip persist.sys.fuse both ways and make sure FuseDaemon
works as expected.
Bug: 140803239

Change-Id: I839a1973c98b4eda982226d20be48d1c08e7464a
diff --git a/Utils.h b/Utils.h
index e0102a7..f607c81 100644
--- a/Utils.h
+++ b/Utils.h
@@ -34,7 +34,7 @@
 namespace android {
 namespace vold {
 
-static const char* kPropFuse = "persist.sys.fuse";
+static const char* kPropFuseSnapshot = "sys.fuse_snapshot";
 
 /* SELinux contexts used depending on the block device type */
 extern security_context_t sBlkidContext;