This reverts commit 4880672a.

Fixes: #1903
Reviewed-by: NMatt Caswell <matt@openssl.org>

GH: #1931

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: NRichard Levitte <levitte@openssl.org>

Split the create_ssl_connection() helper function into two steps: one to
create the SSL objects, and one to actually create the connection. This
provides the ability to make changes to the SSL object before the
connection is actually made.
Reviewed-by: NRichard Levitte <levitte@openssl.org>

This commit adds some session API tests, and in particular tests the
modified behaviour of SSL_set_session() introduced in the last commit. To
do this I have factored out some common code from the asynciotest into a
new ssltestlib.c file. I've also renamed getsettest to sslapitest as this
more closely matches what it now is!
Reviewed-by: NRich Salz <rsalz@openssl.org>

This adds an async IO test. There are two test runs. The first one does
a normal handshake with lots of async IO events. The second one does the
same but this time breaks up all the written records into multiple records
of one byte in length. We do this all the way up until the CCS.
Reviewed-by: NAndy Polyakov <appro@openssl.org>