etcd: do not filter out node TTL

[michaelklishin]

The easiest way to test this is by inspecting the logs.

Using the following rabbitmq.conf:

cluster_formation.peer_discovery_backend = etcd

cluster_formation.etcd.host = localhost
cluster_formation.etcd.port = 2379

cluster_formation.etcd.endpoints.1 = localhost:2379
cluster_formation.etcd.endpoints.2 = localhost:2479

# cluster_formation.etcd.username = rabbitmq
# cluster_formation.etcd.password = rabbitmq

cluster_formation.etcd.key_prefix = example_prefix
cluster_formation.etcd.cluster_name = lolz_cluster

cluster_formation.etcd.node_ttl = 279
cluster_formation.etcd.lock_timeout = 15

log.file.level = debug
log.console.level = debug

and a local etcd node started with all defaults

etcd

and a node with blank data directory started like this

bazel run broker RABBITMQ_ENABLED_PLUGINS="rabbitmq_management,rabbitmq_peer_discovery_etcd" RABBITMQ_NODE_PORT=5672 RABBITMQ_CONFIG_FILE=/path/to/peer_discovery.etcd.7554.conf

you'll see this in the logs

[debug] <0.733.0> etcd peer discovery: acquired a lease 7587869165524620044 for node key /rabbitmq/discovery/rabbitmq/clusters/lolz_cluster/nodes/rabbit@{hostname} with TTL = 279

whereas previously the TTL value would be 61 (the default).

Closes #7554.