doc: add admin api doc
etcdserver: add test for cluster.String
Merge pull request #1384 from jonboulle/test

etcdserver: add test for cluster.String
etcdserver: fix + expand config tests
Merge pull request #1385 from jonboulle/config

etcdserver: fix + expand config tests
Merge pull request #1368 from xiangli-cmu/doc

doc: add admin api doc
etcdserver/etcdhttp: use container for admin/members endpoint
etcdhttp: remove /v2/admin/members/x serving
etcdhttp: rename Members -> members in JSON, update doc