RFR[15] 8238677: java/net/httpclient/ssltest/CertificateTest.java should not specify TLS version

[sha.jiang at oracle.com]

Hi,
java/net/httpclient/ssltest/CertificateTest.java shouldn't use a 
specific TLS version.
And it would be better not to use binary key store files.
Since DSA is not supported by TLSv1.3, this fix also updates the 
certificates to use RSA.

Webrev: http://cr.openjdk.java.net/~jjiang/8238677/webrev.00/
Issue: https://bugs.openjdk.java.net/browse/JDK-8238677

Best regards,
John Jiang