Add a test for BIO_read() returning 0 in SSL_read() (and also for write)

A BIO_read() 0 return indicates that a failure occurred that may be
retryable. An SSL_read() 0 return indicates a non-retryable failure. Check
that if BIO_read() returns 0, SSL_read() returns <0. Same for SSL_write().

The asyncio test filter BIO already returns 0 on a retryable failure so we
build on that.

Reviewed-by: Richard Levitte <levitte@openssl.org>