Standardize RSA private key format

Currently, Kudu stores RSA private keys in PEM format using PEM_write_bio_RSAPrivateKey(), which doesn't specify the format in which the key is stored. It expects it to be PKCS #1 (BEGIN/END RSA PRIVATE KEY), but it seems there are some OpenSSL versions (CryptoComply) that use PKCS #8 instead (BEGIN/END PRIVATE KEY). CryptoTest.RsaPrivateKeyInputOutputPEM fails due to this, as it compares the private key to an expected string, which is in PKCS #1 format. The read functions are explicitly said to handle any known format, so this shouldn't cause any issues, but it would still be nice to standardize on a single format (probably PKCS #8).