Use a new client for the download call.
Add a comment about why we are using a new API client for download.
Add a todo comment.
Merge pull request #1275 from ericsnowcurrently/backups-fix-api-conn

Use a new client for the backups download call.

Apparently an API client is good for only one connection.

(See http://juju-ci.vapour.ws:8080/job/functional-ha-backup-restore/1190/console.)

(Review request: http://reviews.vapour.ws/r/590/)
params.BackupsMetadataResult.UpdateFromMetadata -> apiserver/backups.ResultFromMetadata.
Merge pull request #1264 from ericsnowcurrently/backups-break-cycle

Drop an import-cycle-waiting-to-happen from apiserver/params.

Factor out the UpdateFromMetadata method of params.BackupsMetadataResult into apiserver/backups as ResultFromMetadata. This helps avoid the possibility of import cycles with anything backups imports since apiserver.params is imported in all sorts of places you wouldn't expect.

(Review request: http://reviews.vapour.ws/r/578/)
Drop an error condition unrelated to mongo.
Add a note about what io.EOF means.
Drop "connection is shut down" as well.
Drop the two related tests.
Factor out checkConnectionFailure.
Check for various errnos.