client: return full http.Response in httpActionDo
client: s/transport/CancelableTransport/

CancelableTransport is implemented by callers of the
client pkg, so we should export it so it is
documented publicly.
client: use httpActionDo in httpClusterClient
client: s/newHTTPClusterClient/NewHTTPClient/
client: pass httpActionDo into New[Discovery]KeysAPI
client: pass httpActionDo into NewMembersAPI
client: add httpClusterClient.Sync
etcdctl: sync before running member subcommands
etcdctl: respect --no-sync in member subcommands
client: export necessary interfaces/methods
client: remove unused field
client: elevate context to caller of MembersAPI
client: elevate context to caller of KeysAPI
client: further clarify external interfaces
Merge pull request #1553 from bcwaldon/client-sync

Support syncing and `--no-sync` flag in `etcdctl member` commands