Split slave-bind mount into two.

mount(2) does not work with MS_BIND | MS_SLAVE at a time.
Instead, this CL calls mount twice.

Change-Id: I36b2eb2853f19efc2b0677fb07b6822392aac37c
diff --git a/rootdir/init.rc b/rootdir/init.rc
index 194b41b..32fa4c4 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -271,7 +271,8 @@
     # Mount shared so changes propagate into child namespaces
     mount rootfs rootfs / shared rec
     # Mount default storage into root namespace
-    mount none /mnt/runtime/default /storage slave bind rec
+    mount none /mnt/runtime/default /storage bind rec
+    mount none none /storage slave rec
 
     # Make sure /sys/kernel/debug (if present) is labeled properly
     restorecon_recursive /sys/kernel/debug