init.tuna.rc: Create /storage mountpoint so Dalvik can mark as slave in zygotes

    THIS WAS REVERTED BY CM IN SYSTEM_CORE BECAUSE IT BROKE DEVICES WITH NON-EMULATED STORAGE!

    Mount a tmpfs as /storage in order to create a mountpoint, so that Dalvik
    can later mark /storage as slave in zygotes.  Must use tmpfs as rootfs
    can't be bind mounted (otherwise "mount rootfs /storage /storage bind"
    would work as an alternative).

Change-Id: I638335767b23ef7b7ef926d075339872b5b1229c