etcdserver: add TestRecvSnapshot
*: add testutil pkg
etcdserver: not push ready to readyNode automatically
etcdserver: add TestRecvSlowSnapshot
Merge pull request #1118 from unihorn/133

etcdserver: add TestRecvSnapshot
etcdserver: fix sync tests

This is to fix possible testing failures caused by sync tests.

Changes:
1. Get rid of time sleep operations, which introduces uncertainty.
2. Use fake Store.