Repair downgrade tests

Repair downgrade tests

A number of these tests were failing for the wrong reasons. The intention is to verify
that the client sends an illegal parameter alert when an unexpected downgrade signal
is received. Instead, a number of tests failed because TLS1.1 was not available. The
tests are adapted to explicitly check for an illegal parameter alert from the client.

Client and server flags are updated to enable TLS1.1 where required and a few tests
requiring TLS1.1 were moved to be disabled when TLS1.1 is not available.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/27518)