RFR: JDK-8266802: Shenandoah: Round up region size to page size unconditionally

[Aleksey Shipilev]

Since JDK-8265239, runtime/os/TestTracePageSizes.java fails with Shenandoah like this:


# Internal Error (/home/buildbot/worker/test-jdkX-linux/build/src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp:156), pid=55712, tid=55720
# assert(_num_regions == (max_byte_size / reg_size_bytes)) failed: Must match


This is because Shenandoah region sizes are rounded up to page size only when `ShenandoahUncommit` is true. In the failing test configuration, `ShenandoahUncommit` is false, because Xmx == Xms.

Additional testing:
 - [x] New regression test, now passes
 - [x] `tier1` with Shenandoah

-------------

Commit messages:
 - Minor whitespace
 - Fix and regression tests

Changes: https://git.openjdk.java.net/jdk/pull/3945/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3945&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266802
  Stats: 65 lines in 3 files changed: 60 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3945.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3945/head:pull/3945

PR: https://git.openjdk.java.net/jdk/pull/3945