tools: add async signalfd handler

This provides a Stream<Item = siginfo> via nix' signalfd,
by wrapping it in tokio's PollEvented2 struct to allow
polling via tokio's event loop.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

src/tools.rs

@@ -27,6 +27,7 @@ pub mod ticket;
 pub mod borrow;
 pub mod fs;
 pub mod tty;
+pub mod signalfd;
 
 #[macro_use]
 mod file_logger;