RFR[12] JDK-8206443: Update security libs manual test to cope with removal of javac -source/-target 6

[sha.jiang at oracle.com]

Hi,
JDK-8028563 has removed javac support for 6/1.6 source and target, so 
the following tests has to be updated accordingly.
javax/net/ssl/compatibility/Compatibility.java
sun/security/tools/jarsigner/compatibility/Compatibility.java

In addition, this fix also makes 
javax/net/ssl/compatibility/Compatibility.java can work with JDK 12 builds.

Webrev: http://cr.openjdk.java.net/~jjiang/8206443/webrev.00/
JBS: https://bugs.openjdk.java.net/browse/JDK-8206443

Best regards,
John Jiang