RFR: 8013939: Metaspace capacity not available

[Erik Helin]

Hi all,

this change adds metaspace data to the vm/gc/heap/summary trace event.
The data was missing due to a rewrite of the metaspace API for getting
the capacity and used memory, but has since then been fixed.

Webrev: http://cr.openjdk.java.net/~ehelin/8013939/webrev.00/

Testing:
- JPRT
- Running the GC trace tests

Thanks,
Erik