While investigating 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.