RFR: 8168722: Unified Logging configuration output needs simplifying

[Marcus Larsson]

Hi,

Please review the following patch to make UL configuration descriptions 
more readable/usable. Instead of explicitly listing all tag sets with 
their corresponding levels (a=info,b=info, ..., x=debug, etc), a 
significantly shorter aggregate is now generated and printed instead 
(all=info,x=debug).

Summary:
Initially, the configured level for the majority of the log tag sets is 
found and used for the "all=<level>" part of the config string. Then, 
using a greedy iterative algorithm, selections are generated and added 
to the configuration string to cover the descriptions for tag sets with 
levels deviating from the current description. In each step, the 
selection which covers the most deviating tag sets is chosen. This is 
repeated until there are no deviating tag sets remaining. For the 
curious, the problem can be thought of as a variation of the set cover 
problem [0].

Issue:
https://bugs.openjdk.java.net/browse/JDK-8168722

Webrev:
http://cr.openjdk.java.net/~mlarsson/8168722/webrev.00

Tested with hs-tier 1-2, and locally with 
jtreg/{serviceability,runtime,gc}/logging.

Thanks,
Marcus

[0]: https://en.wikipedia.org/wiki/Set_cover_problem