RFR: 8152905: hs_err file is missing gc threads

[Derek White]

Summary: List the GC threads in the hs_err file in the "Other Threads" 
section

There are 4 small parts to this:
1) Fix G1CollectedHeap::gc_threads_do() to also iterate over concurrent 
mark worker threads.
2) Have Thread::print_on_error() print the thread name of NamedThreads.
3) Factor out code that prints out each "Other Thread" to 
Threads::print_on_error().
4) Call Threads::print_on_error() on every GC thread.

BUG: 8152905: hs_err file is missing gc threads 
<https://bugs.openjdk.java.net/browse/JDK-8152905>
WEBREV: http://cr.openjdk.java.net/~drwhite/8152905/webrev.01/
TESTING:
  - Tested "java -XX:ErrorHandlerTest=1 -version" on all collectors.
  - jprt

Thanks,

  - Derek