RFR: 8177959: G1CollectedHeap::print_on prints incorrect capacity

[Leo Korinth]

Hi,

Remove wrong/inaccurate reporting in print_on() in g1

In g1 -- when printing the memory region used -- the middle value is
incorrectly calculated using (+) instead of (*). Further more, the
middle value in the print does not give precise information. In g1 the
heap is not necessarily contiguous, and holes of non-committed memory
can be present. Thus, instead of fixing the typo, the printout is
modified and the middle value removed.

A more detailed (and verbose) memory usage map is printed in
print_regions_on() and can be obtained with extra flags.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8177959

Webrev:
http://cr.openjdk.java.net/~sjohanss/8177959/00/

Testing:
- JPRT
- Manual check of output

Thanks,
Leo