RFR: 8303921: serviceability/sa/UniqueVtableTest.java timed out

[Alex Menkov]

The change:
- updates UniqueVtableTest to follow standard SA way - attach to target from subprocess and use SATestUtils.addPrivilegesIfNeeded for the subprocess;
- updates several tests in the same directory to resolve NoClassDefFoundError failures; It's known JTReg issue that "@build" actions for part of used shared classes may cause intermittent NoClassDefFoundError in other tests which use the same shared library classpath.

Tested: 100 runs on all platforms, no failures

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Commit messages:
 - UniqueVtableTest

Changes: https://git.openjdk.org/jdk/pull/13030/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13030&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8303921
  Stats: 75 lines in 6 files changed: 37 ins; 22 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/13030.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/13030/head:pull/13030

PR: https://git.openjdk.org/jdk/pull/13030