[8u] RFR (S) 8217315: Proper units should print more significant digits

[Aleksey Shipilev]

Original RFE:
  https://bugs.openjdk.java.net/browse/JDK-8217315
  http://hg.openjdk.java.net/jdk/jdk/rev/d5f6540c6bb1

Unfortunately, 8u does not have support for gtest, which means the new regression test is not usable
there. I worked that around by putting the test into ExecuteInternalVMTests block.

8u webrev:
  http://cr.openjdk.java.net/~shade/8217315/webrev.8u.02/

Testing: hotspot_all, jdk_core; ad-hoc -XX:+ExecuteInternalVMTests run

-- 
Thanks,
-Aleksey