Misc fixes impacting no-tls1_2. Also fixes no-dtls1_2.
Reviewed-by: NRich Salz <rsalz@openssl.org>

Add some more tests for sessions following on from the previous commit
to ensure the callbacks are called when appropriate.
Reviewed-by: NRichard Levitte <levitte@openssl.org>

Reviewed-by: NRich Salz <rsalz@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>