Integrated: [lw5] regression test cleanup, relocation

[Vicente Romero]

cleaning up nullability related test, plus renaming them

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

Commit messages:
 - regression test refactoring, cleanup

Changes: https://git.openjdk.org/valhalla/pull/901/files
 Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=901&range=00
  Stats: 452 lines in 4 files changed: 197 ins; 251 del; 4 mod
  Patch: https://git.openjdk.org/valhalla/pull/901.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/901/head:pull/901

PR: https://git.openjdk.org/valhalla/pull/901