Multi-user external storage support.

Remount rootfs as recursively shared, so that mount changes are
propagated into child namespaces.  Mount external storage for access
from adb.

Clean multi-user dependencies for use in Dalvik.  Also define
external storage paths.

Bug: 6925012
Change-Id: I375de581a63f4f36667894c56a34a9dd45361e8f
diff --git a/rootdir/init.rc b/rootdir/init.rc
index 4c20ec1..5a31a8e 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -128,6 +128,8 @@
 on post-fs
     # once everything is setup, no need to modify /
     mount rootfs rootfs / ro remount
+    # mount shared so changes propagate into child namespaces
+    mount rootfs rootfs / shared rec
 
     # We chown/chmod /cache again so because mount is run as root + defaults
     chown system cache /cache