Adjust tls regress for protocol parsing fixes

This mostly reverts what was done by beck in Tallinn and adjust tlstest
to add new test cases and now failing connection tests.

Revert previous. The added includes were already there. Duh.

Explicitly include fcntl.h and unistd.h for pipe2

Clean up client and server tls{,_config} contexts in tls_test().

Leaks reported by Ilya Shipitsin.

Add a missing circular_init() call in the TLS ordering test.

This makes the regress work correctly again - this was previously masked
by the fact that tls_close() (and hence SSL_shutdown()) was drai

Add a missing circular_init() call in the TLS ordering test.

This makes the regress work correctly again - this was previously masked
by the fact that tls_close() (and hence SSL_shutdown()) was draining the
circular buffer, whereas now we're leaving data behind from a previous
test, resulting in the ordering test failing.

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Add TLS versioning tests.

This ensures that a TLSv1.0, TLSv1.1, TLSv1.2 or TLSv1.3 client can talk
with an appropriately configured server and vice versa.

Remove the now unnecessary tls_init() call.

Add a (currently failing) call to tls_handshake() on a client context that
has not yet been connected. We expect this to fail, but it should fail
gracefully.

Also test calling tls_handshake() on a server connection context that has
already completed a TLS handshake.

Add a test that calls tls_handshake() on a connection that has already
completed a TLS handshake. This should return a failure, but currently
succeeds (hence the regress currently fails).

An an initial sequencing/ordering test for libtls.

Split TLS client/server handshake and close code into separate functions
so that it can be reused.

Move TLS test code into a function that is called from main, making it
easier for new tests to be added.

Free tls_configs earlier now that we have refcounting.

Correctly tls_config_set_ca_file() return value (no effective change).

Spotted by inoguchi@

Add regress tests for libtls, which currently cover handshakes and closes
using callbacks, file descriptors and sockets.