Do not try to run the dispersion bits too early

If the dispersion node is also a storage node or the ring-compute node,
then the dispersion recipe will be run too early, before swift is
totally setup. We detect these cases to not proceed with the dispersion
recipe.
Change element_order

There are two changes:

 1) we want to run swift-dispersion last: it only makes sense to run
    this when swift is fully setup
 2) we move the second pass for swift-storage before swift-proxy. This
    will guarantee that calls to swift-proxy just after it's setup will
    work fine because the storage will be ready.