Avoid false-failures if underlying network connection errors

In Air-Gapped or otherwise network-restricted environments,
   TcpStream::connect can spuriously fail due to name resolution
   failure, or just in establishing the socket itself.

In this situation, the test can't give a meaningful result, and this
failure doesn't indicate a problem in the OpenSSL stack.

Bug: https://github.com/sfackler/rust-openssl/issues/1215