raft: add a test for node.Tick
etcdserver: ensure initial-advertise-peer-urls match initial-cluster

This adds a check to setupCluster to ensure that the list of URLs
specified in `initial-advertise-peer-urls` matches those configured in
`initial-cluster` for this node. Also updates the documentation to
clarify this and address some changes in wording.
etcdserver: move peer URLs check to config
integration: fix test to propagate NewServer errors
raft: stop the node synchronously
integration: remove unnecessary t.Testing argument
Merge pull request #1676 from jonboulle/doc_initial_cluster

etcdserver: validate and document initial-advertise-peer-urls
integration: add increase cluster size test
Merge pull request #1696 from xiang90/testnodetick

raft: add a test for node.Tick
Merge pull request #1664 from yichengq/212

integration: add AddMember test
raft: add a test for node proposal