Reduce log level in RoundRobinLoadBalancer (#2213)

Motivation:
RoundRobinLoadBalancer logs at the warn level if it takes
a host out of rotation due to exceeding the consecutive
failure threshold. The failure maybe retried and/or captured
in metrics/logs by the application and may not necessarily
justify a warn level log from the framework.

Modifications:
- Adjust log level to debug when below the failure threshold,
  and info when crossing the threshold. Note the log level is
  also info when the host is connected to again and taken out
  of the penalty box.

servicetalk-loadbalancer/src/main/java/io/servicetalk/loadbalancer/RoundRobinLoadBalancer.java

@@ -579,7 +579,7 @@ void markUnhealthy(final Throwable cause, final ConnectionFactory<Addr, ? extend
                     final ActiveState nextState = previousState.forNextFailedConnection();
                     if (connStateUpdater.compareAndSet(this, previous,
                             new ConnState(previous.connections, nextState))) {
-                        LOGGER.info("Load balancer for {}: failed to open a new connection to the host on address {}" +
+                        LOGGER.debug("Load balancer for {}: failed to open a new connection to the host on address {}" +
                                         " {} time(s) ({} consecutive failures will trigger health-checking).",
                                 targetResource, address, nextState.failedConnections,
                                 healthCheckConfig.failedThreshold, cause);
@@ -592,7 +592,7 @@ void markUnhealthy(final Throwable cause, final ConnectionFactory<Addr, ? extend
                 final HealthCheck<Addr, C> healthCheck = new HealthCheck<>(connectionFactory, this, cause);
                 final ConnState nextState = new ConnState(previous.connections, healthCheck);
                 if (connStateUpdater.compareAndSet(this, previous, nextState)) {
-                    LOGGER.warn("Load balancer for {}: failed to open a new connection to the host on address {} " +
+                    LOGGER.info("Load balancer for {}: failed to open a new connection to the host on address {} " +
                                     "{} time(s) in a row. Error counting threshold reached, marking this host as " +
                                     "UNHEALTHY for the selection algorithm and triggering background health-checking.",
                             targetResource, address, healthCheckConfig.failedThreshold, cause);