RFR: 8226325: Support building of filtered spec bundles

See this webrev for some enhancements to the documentation-building capabilities of the build system. http://cr.openjdk.java.net/~dlsmith/jdk/8226325/webrev.00

RFR JDK-8226359: Switch to JCov build which supports byte code version 58

Hi, Can you please take a look on a small change to switch to a newer JCov build. This is the whole change: $ hg diff diff -r 17f24c0e2f01 make/conf/jib-profiles.js --- a/make/conf/jib-profiles.js Tue Jun 18 18:38:53 2019 +0100 +++ b/make/conf/jib-profiles.js Tue Jun 18 07:36:23 2019 -0800 @@ -