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.

This is a backport to the stable/icehouse branch for commit SHA
5b2c27a5874c2b5b0a333e4955b03544f6a8119f.

Closes-Bug: 1365350

Conflicts:
	swift/common/db.py
	swift/container/server.py

Change-Id: Id9fca209c9c1216f1949de7108bbe332808f1045
Allow ResellerAdmin role to autocreate accounts
Fix swift-recon --auditor bug

I introduced a bug in swift-recon --auditor, which Christian
Schwede uncovered.  Christian proposed a fix which replaces the
generator nested_get_value with a recursive function which
returns just one instance of a key.  Christian's fix will break
the parallel object auditor patch which uses the generator to
return all instances of a particular key in a nested dictionary
and then sums those values.

This alternative fix sums over all values returned by
nested_get_value, as is done in the parallel auditor patch.

Change-Id: I6ac403395ab42d11161d6df266e8fbd5a2af9a64