Send policy index on async update

Also clean up a couple little things in the object updater. Now it
won't abort processing when it encounters a file (not directory) named
"async_pending-\d+", and it won't process updates in a directory that
does not correspond to a storage policy.

That is, if you have policies 1, 2, and 3, but there's a directory on
your disk named "async_pending-5", the updater will now skip over that
entirely. It won't even bother doing directory listings at all. This
is a good idea, believe it or not, because there's nothing good that
the container server can do with an update from some unknown storage
policy. It can't update the listing, it can't move the object if it's
misplaced... all it can do is ignore the request, so it's better to
just not send it in the first place. Plus, if this is due to a
misconfiguration on one storage node, then the updates will get
processed once the configuration is fixed.

Change-Id: Ic645ac3426e18adfc8c46613c8aadcf765d6d0e2
Send policy index to container on sync update

We're sending the policy index to the container on async update, so we
really should send it on synchronous update (object-server ==>
container-server) as well.

Also cleaned up a couple of unrelated test mocks to use the 'mock'
library instead of hand-patching.

Change-Id: I776ff8b519a7bef441466d199137d8a315600973