External replication refactoring #256

Job	Run time
Build images	10s
test (GODOG_FEATURE=active_nodes.feature make test)	8m 27s
test (GODOG_FEATURE=async.feature make test)	4m 52s
test (GODOG_FEATURE=cascade_replicas.feature make test)	7m 26s
test (GODOG_FEATURE=CLI.feature make test)	4m 41s
test (GODOG_FEATURE=crash_recovery.feature make test)	5m 7s
test (GODOG_FEATURE=events_reenable.feature make test)	2m 26s
test (GODOG_FEATURE=failover.feature make test)	12m 49s
test (GODOG_FEATURE=free_space.feature make test)	6m 31s
test (GODOG_FEATURE=host_discovery.feature make test)	3m 22s
test (GODOG_FEATURE=host_management.feature make test)	3m 30s
test (GODOG_FEATURE=maintenance.feature make test)	5m 13s
test (GODOG_FEATURE=offline_mode.feature make test)	3m 4s
test (GODOG_FEATURE=priority.feature make test)	6m 18s
test (GODOG_FEATURE=readonly_filesystem.feature make test)	2m 26s
test (GODOG_FEATURE=recovery.feature make test)	3m 26s
test (GODOG_FEATURE=repair.feature make test)	10m 33s
test (GODOG_FEATURE=statefile.feature make test)	4m 29s
test (GODOG_FEATURE=switchover_from.feature make test)	11m 18s
test (GODOG_FEATURE=switchover_to.feature make test)	11m 12s
test (GODOG_FEATURE=zk_failure.feature make test)	7m 48s
test (GODOG_FEATURE=zk_maintenance.feature make test)	4m 37s
	2h 9m 45s

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