Tests: improved compatibility when using recent "openssl" app. Starting with OpenSSL 3.0, "openssl genrsa" generates encrypted keys in PKCS#8 format instead of previously used PKCS#1 format. Further, since OpenSSL 1.1.0 such keys are using PBKDF2 hmacWithSHA256. Such keys are not supported by old SSL libraries, notably by OpenSSL before 1.0.0 (OpenSSL 0.9.8 only supports hmacWithSHA1) and by BoringSSL before May 21, 2019 (support for hmacWithSHA256 was added in 302a4dee6c), and trying to load such keys into nginx compiled with an old SSL library results in "unsupported prf" errors. To facilitate testing with old SSL libraries, keys are now generated with "openssl genrsa -traditional" if the flag is available.