etcd: Add TTL support to etcd_mock
etcd: Add TTL support to etcd_mock

We weren't able to properly test code that required a TTL before
since our mocked out version of etcd didn't support it. This patch
adds that support.

stevenlin598/quilt,stevenlin598/quilt,quilt/quilt,tejasmanohar/quilt,mmussomele/quilt,NetSys/quilt,stevenlin598/quilt,mmussomele/quilt,PenguinToast/quilt,LuiseV/quilt,kelda/kelda,PenguinToast/quilt,mmussomele/quilt,LuiseV/quilt,kklin/quilt,kklin/kelda,kklin/kelda,mmussomele/quilt,NetSys/quilt,stevenlin598/quilt,stevenlin598/quilt,kelda/kelda,quilt/quilt,NetSys/quilt,kklin/kelda,kklin/quilt,LuiseV/quilt,tejasmanohar/quilt,LuiseV/quilt,NetSys/quilt,PenguinToast/quilt,PenguinToast/quilt,mmussomele/quilt,LuiseV/quilt,kayousterhout/quilt,tejasmanohar/quilt,tejasmanohar/quilt,kayousterhout/quilt,ejj/quilt-dev,kklin/quilt,kklin/kelda,stevenlin598/quilt,quilt/quilt,NetSys/quilt,quilt/quilt,ejj/quilt-dev,kklin/quilt,kayousterhout/quilt,kayousterhout/quilt,ejj/quilt-dev,mmussomele/quilt,ejj/quilt-dev,kelda/kelda,kelda/kelda,PenguinToast/quilt