RFR: 8293282: LoadLibraryUnloadTest.java fails with "Too few cleared WeakReferences"

[Roger Riggs]

Modify the LoadLibraryUnload test to call gc() more a few times, allowing multiple gc cycles to queue the expected refs.
Short the timeout on each cycle to 10 sec.

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

Commit messages:
 - Add bugid to LoadLibraryUnloadTest
 - Modify the wait loop to repeat the System.gc and count queued refs.

Changes: https://git.openjdk.org/jdk/pull/10223/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10223&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293282
  Stats: 9 lines in 2 files changed: 3 ins; 3 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/10223.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10223/head:pull/10223

PR: https://git.openjdk.org/jdk/pull/10223