Add new ssl_test option.

Add option ExpectedTmpKeyType to test the temporary key the server
sends is of the correct type.

Reviewed-by: Kurt Roeckx <kurt@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2191)
(cherry picked from commit b93ad05d)