intermittent? parallel/test-http2-session-unref failure on sharedlibs debug

[mhdawson]

• Version: master
• Platform: ubuntu1604_sharedlibs_debug
• Subsystem: http2

https://ci.nodejs.org/job/node-test-commit-linux-containered/1965/nodes=ubuntu1604_sharedlibs_debug_x64/console

11:01:46 not ok 1025 parallel/test-http2-session-unref
11:01:46   ---
11:01:46   duration_ms: 9.18
11:01:46   severity: fail
11:01:46   stack: |-
11:01:46     (node:12269) ExperimentalWarning: The http2 module is an experimental API.
11:01:46     assert.js:74
11:01:46       throw new AssertionError(obj);
11:01:46       ^
11:01:46     
11:01:46     AssertionError [ERR_ASSERTION]: () => {} at /home/iojs/build/workspace/node-test-commit-linux-containered/nodes/ubuntu1604_sharedlibs_debug_x64/test/parallel/test-http2-session-unref.js:53
11:01:46         at Timeout.mustNotCall (/home/iojs/build/workspace/node-test-commit-linux-containered/nodes/ubuntu1604_sharedlibs_debug_x64/test/common/index.js:539:12)
11:01:46         at ontimeout (timers.js:438:11)
11:01:46         at Timer.unrefdHandle (timers.js:524:7)
11:01:46   ...