RFR(xs): 8199430: Rename MetaspaceAux to something more meaningful

[Thomas Stüfe]

Hi all, may I please have reviews and a sponsor for the following small
change:

bug: https://bugs.openjdk.java.net/browse/JDK-8199430
webrev:
http://cr.openjdk.java.net/~stuefe/webrevs/8199430-rename-metaspace-aux/webrev.00/webrev/

This is a very simple straightforward rename. Why discussing 8185034,
Coleen expressed the wish for a better name for MetaspaceAux. So, this is
what this change does.

Thanks, Thomas