Add ssl_certs test fixture and delete cert files

Co-authored-by: dotlambda <6806011+dotlambda@users.noreply.github.com>

Also in gen.sh don't c_rehash certs (certs dir does not exist) and refer to openssl.cnf relative to gen.sh's location (not the current dir)

Update gen.sh

Don't need to specify sh

Read openssl.cnf in parent dir of bash script, not cwd

Bug fixes

Use tmp_path_factory

Update conftest.py

shell=True

check not check_output in subprocess.run

Don't c_rehash certs