Investigate flaky test-http2-session-timeout #20628

03:10:22 not ok 2130 sequential/test-http2-session-timeout
03:10:22   ---
03:10:22   duration_ms: 1.252
03:10:22   severity: fail
03:10:22   exitcode: 1
03:10:22   stack: |-
03:10:22     (node:6609) ExperimentalWarning: The http2 module is an experimental API.
03:10:22     assert.js:77
03:10:22       throw new AssertionError(obj);
03:10:22       ^
03:10:22     
03:10:22     AssertionError [ERR_ASSERTION]: function should not have been called at /home/iojs/build/workspace/node-test-commit-linux-containered/nodes/ubuntu1604_sharedlibs_openssl110_x64/test/sequential/test-http2-session-timeout.js:11
03:10:22         at Http2Server.mustNotCall (/home/iojs/build/workspace/node-test-commit-linux-containered/nodes/ubuntu1604_sharedlibs_openssl110_x64/test/common/index.js:540:12)
03:10:22         at Http2Server.emit (events.js:182:13)
03:10:22         at ServerHttp2Session.sessionOnTimeout (internal/http2/core.js:2526:15)
03:10:22         at Object.onceWrapper (events.js:273:13)
03:10:22         at ServerHttp2Session.emit (events.js:182:13)
03:10:22         at ServerHttp2Session._onTimeout (internal/http2/core.js:1256:10)
03:10:22         at ontimeout (timers.js:428:11)
03:10:22         at tryOnTimeout (timers.js:291:5)
03:10:22         at listOnTimeout (timers.js:252:5)
03:10:22         at Timer.processTimers (timers.js:212:10)
03:10:22   ...