pkg/blobserver/encrypt: Log time it takes to read encryption metadata.

We'll use this later on to see the effect of using blob streaming
rather than enumeration. In particular, we will be looking for a
significant speed-up with diskpacked when metadata processing uses
streaming rather than enumeration.

Change-Id: I8295d05d74a84518844237bc48d4f11db8ea14b0
Rewrite Picasa importer for the new Importer API

Change-Id: I0789f4732412aa559078ec2c6b6797925ab8cd05