RFR: 8253794: TestAbortVMOnSafepointTimeout never timeouts [v2]

[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.

Robbin Ehn has updated the pull request incrementally with one additional commit since the last revision:

  Update with input from reviews

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/465/files
  - new: https://git.openjdk.java.net/jdk/pull/465/files/13b40338..90fb3106

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=465&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=465&range=00-01

  Stats: 34 lines in 3 files changed: 12 ins; 15 del; 7 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