etcd: remove assertion when creating bucket and value with the same key

This commit removes an assertion which is not needed because with etcd
we can safely create keys and values with the same key since they are
stored under different keys in the DB. This saves us one unnecessary Get
on every Put.

kvdb/debug.go

@@ -0,0 +1,8 @@
+// +build dev
+
+package kvdb
+
+const (
+	// Switch on extra debug code.
+	etcdDebug = true
+)