Show the sum of every policy's amount in /recon/async

After the release of Swift ver. 2.0.0, some recon responses do not
show each policy's information yet. To make things worse, some recon
results only count on policy-0's score, therefore the total is not
shown in the recon results.

With this patch, async_pending count of recon results becomes
policy-aware. Suppose a number of async_pending files for policy-0 is 2
and a number for policy-1 is 3, recon sums up every policy's amount
as follows.

$ curl http://<host>:<port>/recon/async
{"async_pending": 5} # It showed 2 before this commit

Related-Bug: 1375332
Change-Id: Ifc88b8c9e06b9f022a926a87ed807e938e1e0412