Skip legacy TLS 1.0 / TLS 1.1 tests if disabled by system

[clue]

Skip legacy TLS 1.0 / TLS 1.1 tests if disabled by system. For example, this affects a current Ubuntu 20.04 installation which appears to prohibit legacy TLS connections.

The same bug can be reproduced in curl with $ curl -s --tlsv1 -v https://tls-v1-0.badssl.com:1010/ at the time of writing this. This seems to be addressed in curl with curl/curl#4097 and curl/curl#4304. PHP appears to apply a similar logic, but it still fails at the moment (https://github.com/php/php-src/blob/8e9bc90004f09a0d67fdac393a8f3fca904be397/ext/openssl/xp_ssl.c#L1760 vs https://github.com/ruby/openssl/blob/4b43ffc1292eeb70ff886847836e21ad96ed8796/ext/openssl/ossl_ssl.c#L162-L195).

For PHP, this can be reproduced (prior to applying this patch) by running the test suite in a default Ubuntu installation (PHP 7.4.3):

$ docker run -it --rm -v `pwd`:/data --workdir=/data ubuntu:20.04 bash
# apt update && apt install -y php-cli php-xml php-mbstring ca-certificates
# vendor/bin/phpunit