Support kernel.net_ticktime in Cuttlefish configuration (master)

[acogoluegnes]

net_ticktime, if present in the .conf file, is set up with net_kernel:set_net_ticktime/1 before the configuration of the .conf file is applied to the other applications. The kernel application is already running when the configuration is applied, so net_ticktime is set in a specific way.

Fixes #1522

[michaelklishin]

I discovered the following during manual testing: since the transition period by default takes 60 seconds, should a CLI tool contact a running node with net_ticktime in the .conf file with this PR, it will fail with something like this:

Stopping and halting node rabbit@warp10 ...
Error:
function_clause
 Stacktrace [{net_kernel,set_net_ticktime,
                         [{ongoing_change_to,20},0],
                         [{file,"net_kernel.erl"},{line,195}]},
             {rabbit_misc,rpc_call,5,
                          [{file,"src/rabbit_misc.erl"},{line,1175}]},
             {'Elixir.RabbitMQCtl',maybe_run_command,3,
                                   [{file,"lib/rabbitmqctl.ex"},{line,113}]},
             {'Elixir.RabbitMQCtl','-exec_command/2-fun-0-',5,
                                   [{file,"lib/rabbitmqctl.ex"},{line,80}]},
             {'Elixir.RabbitMQCtl',main,1,
                                   [{file,"lib/rabbitmqctl.ex"},{line,43}]},
             {'Elixir.Kernel.CLI','-exec_fun/2-fun-0-',3,
                                  [{file,"lib/kernel/cli.ex"},{line,76}]}]

because CLI tools temporarily tweak node's net_ticktime for the two values to be in sync.

We can try a transition period of 0 but I don't know what complications can stem out of that. I don't think the change is worth the risk since it's a minor convenience improvement.

[michaelklishin]

A correction: it's not just CLI tools, it's any code that uses rabbit_misc:rpc_call/5 but it should not be used on any hot code path.

Updating that function to support transition periods should be sufficient. It can still potentially be a breaking change for the environment where CLI tools use a significantly higher tick time value vs. the server: the server would then detect inactivity on an idle connection much earlier than the CLI tool. We don't have a lot of reports about that, though, possibly because CLI tool connections do go inactive for long enough periods of time.

[michaelklishin]

According to rabbitmq/rabbitmq-common#60, that function is used by management and possibly other plugins.