FakeEtcdClient: Maintain change index
Generate modification index only if f.TestIndex is specified.
This is for compatibility with existing tests.
Fail immediately if f.Err is set
return EtcdErrorNodeExist when Create is called for existing node
Implement FakeEtcdClient.CompareAndSwap
AtomicUpdate should use api.Encode
Implement FakeEtcdClient.ExpectNotFoundGet
Add test for AtomicUpdate
Merge pull request #717 from nyaxt/atomicupdate_test

Add test for AtomicUpdate