Use the new certificates/chains in regress.

The new certificates are more representative of the real world. The old
certificates use weak algorithms and expire in the very near future. Most
of our r

Use the new certificates/chains in regress.

The new certificates are more representative of the real world. The old
certificates use weak algorithms and expire in the very near future. Most
of our regress has already been switched over, this changes the remainder.

Thanks to Bernhard M. Wiedemann for reminding us of the upcoming expiry.

ok tb@

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

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