Add a test to check the EC point formats extension appears when we expect

The previous commit fixed a bug where the EC point formats extensions did
not appear in the ServerHello. This should have been caught by
70-test_sslmessages but that test never tries an EC ciphersuite. This
updates the test to do that.

Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2153)