RFR: Ensure vthread has connected to server [v2]

[Miao Zheng]

> I have run the test case of InterruptHttp.java in fast debug version of jdk with options:
> -XX:+UseG1GC  -XX:+ScavengeALot -XX:ScavengeALotInterval=200 -XX:-GCALotAtAllSafepoints
> 
> And the test case failed, The output is "Execution failed: `main' threw exception: java.lang.RuntimeException: Expected 1 HTTP connection"
> 
> The reason is Thread.sleep(1000) can not ensure that vthread has connected to server when using some options and fastdebug version of jdk.
> 
> So, I fix this to ensure vthread has connected to server.

Miao Zheng has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  Ensure vthread has connected to server

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

Changes:
  - all: https://git.openjdk.java.net/loom/pull/60/files
  - new: https://git.openjdk.java.net/loom/pull/60/files/308ad7f7..b37dcf1e

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=loom&pr=60&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=loom&pr=60&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/loom/pull/60.diff
  Fetch: git fetch https://git.openjdk.java.net/loom pull/60/head:pull/60

PR: https://git.openjdk.java.net/loom/pull/60