Make the Syncgroup factory methods like the ones for Collection

There is currently a Database.Syncgroup(wire.Id) factory method,
change it to be consistent with Collection.SyncgroupForId/Syncgroup,
where Syncgroup() takes a name and context and the user blessing
is pulled from the context.

MultiPart: 3/3
Change-Id: Ie63e86c57721f77c3e011aec6a531d0928ec180f
diff --git a/go/src/v.io/x/sensorlog/internal/client/device.go b/go/src/v.io/x/sensorlog/internal/client/device.go
index 65215e2..106d649 100644
--- a/go/src/v.io/x/sensorlog/internal/client/device.go
+++ b/go/src/v.io/x/sensorlog/internal/client/device.go
@@ -48,7 +48,7 @@
 	// really relevant until syncgroup Leave is implemented.
 	sgMemberInfo := wire.SyncgroupMemberInfo{SyncPriority: config.SyncPriority}
 	sgId := wire.Id{Name: devSgName, Blessing: "blessing"}
-	if _, err := db.Syncgroup(sgId).Join(ctx, sgPublishSb, "", sgMemberInfo); err != nil {
+	if _, err := db.SyncgroupForId(sgId).Join(ctx, sgPublishSb, "", sgMemberInfo); err != nil {
 		return nil, err
 	}
 
diff --git a/go/src/v.io/x/sensorlog/internal/measure/syncgroup.go b/go/src/v.io/x/sensorlog/internal/measure/syncgroup.go
index 759e53f..5b90f4b 100644
--- a/go/src/v.io/x/sensorlog/internal/measure/syncgroup.go
+++ b/go/src/v.io/x/sensorlog/internal/measure/syncgroup.go
@@ -89,5 +89,5 @@
 	}
 	sgMemberInfo := wire.SyncgroupMemberInfo{SyncPriority: config.SyncPriority}
 
-	return db.Syncgroup(sgId).Create(ctx, sgSpec, sgMemberInfo)
+	return db.SyncgroupForId(sgId).Create(ctx, sgSpec, sgMemberInfo)
 }