Assume a private key is RSA if the header does not specify a type.
Auto-generated certificates are RSA, but the header does not indicate
this (e.g. BEGIN PRIVATE KEY). Since the type is not specified,
the certificate was not being parsed correctly, and attempts to
connect over HTTPS failed and caused web browser errors.
Fixes "ERR_SSL_VERSION_OR_CIPHER_MISMATCH" in Chrome.
Fixes "ssl_error_no_cypher_overlap" in Firefox.