(feat) Use poll instead of select for tcp connections

[killme2008]

Use poll to replace select for creating a TCP connection on *nix platform, fixed rust-lang/libc#1401

Because select has an upper limit as FD_SETSIZE, and if the process has many file descriptors, it will panic at

fd_set.insert(socket_fd);

The backtrace:

0:     0x55d9ba51486d - backtrace::backtrace::libunwind::trace::h5d5f7561c1a9102a
                        at /root/.cargo/registry/src/mirrors.ustc.edu.cn-12df342d903acd47/backtrace-0.2.3/src/backtrace/libunwind.rs:54
                         - backtrace::backtrace::trace::h1a0e9cf6143fd38a
                        at /root/.cargo/registry/src/mirrors.ustc.edu.cn-12df342d903acd47/backtrace-0.2.3/src/backtrace/mod.rs:70
   1:     0x55d9ba514512 - backtrace::capture::Backtrace::new::h5f5871afa8f4b8c8
                        at /var/lib/docker/volumes/jenkins-slave-2/_data/workspace/ceresdb.datanode/target/release/build/backtrace-885d76ac7e31444c/out/capture.rs:79- <backtrace::capture::Backtrace as core::default::Default>::default::hebc8b9531935d674
                        at /var/lib/docker/volumes/jenkins-slave-2/_data/workspace/ceresdb.datanode/target/release/build/backtrace-885d76ac7e31444c/out/capture.rs:187 cse::engine::util::set_exit_hook::{{closure}}::ha6e6efad2fa08800
                        at src/engine/util/mod.rs:148
   3:     0x55d9ba5e78c9 - std::panicking::rust_panic_with_hook::h744417edfe714d72
                        at src/libstd/panicking.rs:482
   4:     0x55d9ba5e7371 - std::panicking::continue_panic_fmt::h3557b3c3fa21b47b
                        at src/libstd/panicking.rs:385
   5:     0x55d9ba5e7255 - rust_begin_unwind
                        at src/libstd/panicking.rs:312
   6:     0x55d9ba60224c - core::panicking::panic_fmt::h74ee8034b317ceed
                        at src/libcore/panicking.rs:85
   7:     0x55d9ba602200 - core::panicking::panic_bounds_check::h34b80e64d41db052
                        at src/libcore/panicking.rs:61
   8:     0x55d9ba3ee631 - libc::unix::notbsd::FD_SET::ha619521f92708798
                        at /root/.cargo/registry/src/mirrors.ustc.edu.cn-12df342d903acd47/libc-0.2.58/src/unix/notbsd/mod.rs:1177
                         - nix::sys::select::FdSet::insert::h098df705361b8e98
                        at /root/.cargo/registry/src/mirrors.ustc.edu.cn-12df342d903acd47/nix-0.11.1/src/sys/select.rs:26
   9:     0x55d9ba0eed63 - mysql::io::tcp::connect_fd_timeout::hd42bf0ea22ab5998

[blackbeam]

Thanks!