std::rt::uv::net: Handle `read_start` error

cc #9605
std::rt: Add NotConnected to IoErrorKind
rt::io::net::tcp: Fix eof_twice tests on Win32

cc #8811
auto merge of #9721 : klutzy/rust/uv-net-read-fix, r=alexcrichton

See #9605 for detailed information.

This also fixes two tests of #8811.