RFR: 8284233: serviceability/jvmti/vthread/InterruptThreadTest/InterruptThreadTest.java failing in loom repo [v2]

[Serguei Spitsyn]

> The test has a lack of synchronization.
> The fix is to wait for target virtual thread reaching the desired state of execution.
> The fix is being tested with 100 of mach5 test runs on all platforms.

Serguei Spitsyn has updated the pull request incrementally with two additional commits since the last revision:

 - removed one more cause of timeouts
 - restored one line of tracing

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

Changes:
  - all: https://git.openjdk.java.net/loom/pull/169/files
  - new: https://git.openjdk.java.net/loom/pull/169/files/bbec7ed6..56a2422b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=loom&pr=169&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=loom&pr=169&range=00-01

  Stats: 9 lines in 1 file changed: 0 ins; 2 del; 7 mod
  Patch: https://git.openjdk.java.net/loom/pull/169.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/169/head:pull/169

PR: https://git.openjdk.java.net/loom/pull/169