Two small account-quota fixes

First: even if a user has exceeded their account quota, they should be
able to make object POST requests. Updating an object's metadata isn't
going to make them any more over quota, so should be allowed.

Second: don't bother with the reseller_admin check for container or
object requests. If I send the header X-Account-Meta-Quota-Bytes: 100
on e.g. an object PUT request, the proxy will (rightly) ignore it. Now
account-quotas does too.

Change-Id: I970a76349659acdd8229a324bd33bfe7fe7261a4
Merge "Two small account-quota fixes"