Fix metadata overall limits bug

Currently metadata limits are checked on a per request basis. If
multiple requests are sent within the per request limits, it is
possible to exceed the overall limits.  This patch adds an overall
metadata check to ensure that multiple requests to add metadata to
an account/container will check overall limits before adding
the additional metadata.

Change-Id: Ib9401a4ee05a9cb737939541bd9b84e8dc239c70
Closes-Bug: 1365350
Merge "Fix metadata overall limits bug"