RFR: 8366298: FDLeakTest sometimes takes minutes to complete on Linux [v3]

[Stefan Karlsson]

> While investigating [JDK-8260555](https://bugs.openjdk.org/browse/JDK-8260555), which lowers the timeout factor from 4 to 1, we found that FDLeakTest sometimes times out on Linux.
> 
> The reason is that the test performs a `fcntl` call for each and every potential file descriptor number. This can be a large number of calls and sometimes results in minutes-long test executions.
> 
> I propose that we fix this by limiting the max number of open file descriptors. This lowers the test execution time to about 1 second.
> 
> The test has two processes. One that executes the libFDLeaker.c code below as an agent in the test JVM, then it forks into a exeFDLeakTester.c, which reads the property `int max_fd = (int)sysconf(_SC_OPEN_MAX);`. The setting of `RLIMIT_NOFILE` to `100` lowers `max_fd` to `100`. I've verified this on both Linux and on macOS.
> 
> I've run the test manually on Linux and macOS and verified that it runs faster. I've also run this through tier1.

Stefan Karlsson has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - Remove jtreg timeouts
 - Merge remote-tracking branch 'upstream/master' into 8366298_fdleaktest
 - Add error logging
 - 8366298: FDLeakTest sometimes takes minutes to complete on Linux

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/26979/files
  - new: https://git.openjdk.org/jdk/pull/26979/files/78fbf6d7..382647c3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=26979&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=26979&range=01-02

  Stats: 12952 lines in 682 files changed: 9828 ins; 855 del; 2269 mod
  Patch: https://git.openjdk.org/jdk/pull/26979.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26979/head:pull/26979

PR: https://git.openjdk.org/jdk/pull/26979