Store container names in memdb

Currently, names are maintained by a separate system called "registrar".
This means there is no way to atomically snapshot the state of
containers and the names associated with them.

We can add this atomicity and simplify the code by storing name
associations in the memdb. This removes the need for pkg/registrar, and
makes snapshots a lot less expensive because they no longer need to copy
all the names. This change also avoids some problematic behavior from
pkg/registrar where it returns slices which may be modified later on.

Note that while this change makes the *snapshotting* atomic, it doesn't
yet do anything to make sure containers are named at the same time that
they are added to the database. We can do that by adding a transactional
interface, either as a followup, or as part of this PR.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

daemon/daemon_test.go

@@ -12,7 +12,6 @@ import (
 	"github.com/docker/docker/container"
 	_ "github.com/docker/docker/pkg/discovery/memory"
 	"github.com/docker/docker/pkg/idtools"
-	"github.com/docker/docker/pkg/registrar"
 	"github.com/docker/docker/pkg/truncindex"
 	"github.com/docker/docker/volume"
 	volumedrivers "github.com/docker/docker/volume/drivers"
@@ -65,10 +64,15 @@ func TestGetContainer(t *testing.T) {
 	index.Add(c4.ID)
 	index.Add(c5.ID)
 
+	containersReplica, err := container.NewViewDB()
+	if err != nil {
+		t.Fatalf("could not create ViewDB: %v", err)
+	}
+
 	daemon := &Daemon{
-		containers: store,
-		idIndex:    index,
-		nameIndex:  registrar.NewRegistrar(),
+		containers:        store,
+		containersReplica: containersReplica,
+		idIndex:           index,
 	}
 
 	daemon.reserveName(c1.ID, c1.Name)