RFR: 8290812: Add a test for ResourceHashtable

[Coleen Phillimore]

I added a test for ResourceHashtable to show the interactions with it and Symbol* refcounting.
Tested with tier1 on Oracle platforms.

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

Commit messages:
 - fix wording
 - 8290812: Add a test for ResourceHashtable

Changes: https://git.openjdk.org/jdk/pull/9603/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9603&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8290812
  Stats: 100 lines in 1 file changed: 99 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/9603.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9603/head:pull/9603

PR: https://git.openjdk.org/jdk/pull/9603