Fix process management

b6cf01a4 refactor: make path to std::process::exit shorter

This patch reduces the variable passing trace length. Instead of returning it from function to function, call exit() in place.

The trace of exit code before the patch:

std::process::exit() <- main <- main_run <- fork(child) <- tarantool_main

And now:

std::process::exit() <- tarantool_main

The type safety is ensured at compilation time by using ! type for fn main(). See https://doc.rust-lang.org/reference/types/never.html

5b5d25f3 Handle supervisor termination in child

Handle supervisor termination in child

We don't want a child process to live without the supervisor.

Usually, supervisor waits for child forever and retransmits termination signals. But if the parent is killed with a SIGKILL there's no way to pass anything.

This patch supplies a child process with a supervisor_fuse fiber. It tries to read from a pipe (that supervisor never writes to), and if the writing end is closed, it means the supervisor has terminated. In this case, child process terminates too.

Part of #56 (closed)

c3af1724 Forward signals from supervisor to child

That's it.

Close #56 (closed)