Switch to docker registry v2

With docker 1.10, the v2 registry finally has decent performances.

TrivialFix

Change-Id: I85fde385dba3579abad497e327170d30b8b9fc7c

dev/vagrant/centos-bootstrap.sh

@@ -140,7 +140,7 @@ EOF
             -e MIRROR_SOURCE_INDEX=https://index.docker.io \
             -e STORAGE_PATH=/var/lib/registry \
             -v /data/host/registry-storage:/var/lib/registry \
-            registry:0.9.1
+            registry:2
     fi
 }