Allow the zygote to create instruction set specific
directories under /data/dalvik-cache and to change their owner
to the system UID.

These subdirectories are required in order to support
instruction set specific dex caches on devices that support
multiple instruction sets. We can't ask init to create these
directories for us, because init doesn't have any knowledge
about the list of runtime instruction sets the device supports.

The owner needs to be system because the package manager (running
in the system_server) is allowed to manipulate files under this
directory.

Change-Id: Ibb248d198d4430ef8bc494111a60d537c7d04784