RFR: JDK-8175845 Provide javadoc descriptions for jdk.hotspot.agent module

[Ujwal Vangapally]

Kindly review this small change

https://bugs.openjdk.java.net/browse/JDK-8175845
webrev: 
http://cr.openjdk.java.net/~uvangapally/webrev/2017/8175845/webrev.00/

Thanks,

Ujwal.