RFR 8191810: jjs should avoid hard coded javadoc base url for shift-tab documentation feature

[Sundararajan Athijegannathan]

Please review.

Bug: https://bugs.openjdk.java.net/browse/JDK-8191810
Webrev: http://cr.openjdk.java.net/~sundar/8191810/webrev.00/

Thanks,
-Sundar