use a common etcd component library for coordination tasks

api.go

coordination/etcdtest/fake_etcd.go

coordination/masterelection/masterelection.go

coordination/masterelection/masterelection_test.go

coordination/presence/cache.go

coordination/presence/presence.go

coordination/watcher/cache.go

coordination/watcher/sync.go

coordination/watcher/watcher.go

coordination/watcher/watcher_test.go

etcd_client.go

fe/http_test.go

node/icecast_config_test.go

node/node.go

node/node_test.go