Keep Etcd dependencies to `Clustering::Controller` #4937

Job	Run time
Compile LavinMQ	1m 1s
Format check	12s
Spec FreeBSD	3m 5s
Lint check	1m 3s
Lint javascript	16s
Lint OpenAPI	14s
Spec	1m 55s
Filters for frontend specs	6s
Spec OS X	2m 11s
Test in release mode	16s
RabbitMQ HTTP API Go client test	59s
RabbitMQ java client test	5m 8s
Bunny client test	2m 30s
RabbitMQ HTTP API Ruby client test	59s
Frontend specs	0s
	19m 55s

Provide feedback