RFR: Improve and unify the printout format for the g1HRPrinter.

[David Lindholm]

Hi,

Please review this patch that unifies the format of the printouts 
printed by the g1HRPrinter. It also gets the typestring of the 
HeapRegion from the HeapRegion itself.


Bug: https://bugs.openjdk.java.net/browse/JDK-8145301
Webrev: http://cr.openjdk.java.net/~david/JDK-8145301/webrev.00/

Testing: JPRT


Thanks,
David