RFR: 8253794: TestAbortVMOnSafepointTimeout never timeouts

[Robbin Ehn]

The issue is that this test doesn't consider Handshake All operation.
Depending if/when such operation is scheduled it can lockup the VM thread.
And the safepoint that should timeout never happens.
See issue for more information.

So I changed the test to "try timeout" the safepoint, but if there was no safepoint (blocked by a handshake all), we
retry. We sleep unsafe much longer than the interval SafepointALot generates operations, which 'guarantees' we will
timeout if there is no handshake all. (some extreme case of kernel scheduling causing a very long context switch could
also make us not timeout)

Passes t1, t3, and repeat runs of the test.

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Commit messages:
 - Fixed test

Changes: https://git.openjdk.java.net/jdk/pull/465/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=465&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253794
  Stats: 53 lines in 3 files changed: 16 ins; 26 del; 11 mod
  Patch: https://git.openjdk.java.net/jdk/pull/465.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/465/head:pull/465

PR: https://git.openjdk.java.net/jdk/pull/465