cmake: wrap the symbols used in the "ssl-cert-paths-discover" test

Wrap the symbols used in the "ssl-cert-paths-discover" test to
avoid clashes.

Symbols from openssl have been wraped to:

    crypto_X509_get_default_cert_dir_env
    crypto_X509_get_default_cert_file_env

Tarantool symbols have been prefixed by "tnt_":

    tnt_ssl_cert_paths_discover
    tnt_default_cert_dir_paths
    tnt_default_cert_file_paths

Part of #5932