Fix failing test on Windows

[mcdallas]

This test fails on windows with error:

test peer_handshake ... FAILED

failures:

---- peer_handshake stdout ----
thread 'peer_handshake' panicked at 'called `Result::unwrap()` on an `Err` value: Os { code: 10049, kind: AddrNotAvailable, message: "The requested address is not valid in its context." }', libcore\result.rs:1009:5
note: Run with `RUST_BACKTRACE=1` for a backtrace.

This change fixes it and shouldn't change the behavior because we are already listening on localhost only

grin/p2p/tests/peer_handshake.rs

Line 35 in 79c97c3

let listener = TcpListener::bind("127.0.0.1:0").unwrap();