Investigate flake test-worker-debug on ubuntu shared libs

Flakes below. May be flaky on other platforms, post here if anyone sees that.

See: #28232 (comment)

13:09:51 not ok 2248 parallel/test-worker-debug
13:09:51   ---
13:09:51   duration_ms: 0.917
13:09:51   severity: fail
13:09:51   exitcode: 1
13:09:51   stack: |-
13:09:51     Test basic debug scenario
13:09:51     This is a message from a worker
13:09:51     Test disabling attach to workers
13:09:51     This is a message from a worker
13:09:51     Test disabled waitForDebuggerOnStart
13:09:51     Test attach to a running worker and then start a new one
13:09:51     This is a message from a worker
13:09:51     Test NodeRuntime.waitForDisconnect in worker
13:09:51     Mismatched noop function calls. Expected exactly 1, actual 0.
13:09:51         at Object.mustCall (/home/iojs/build/workspace/node-test-commit-linux-containered/test/common/index.js:340:10)
13:09:51         at Object.<anonymous> (/home/iojs/build/workspace/node-test-commit-linux-containered/test/parallel/test-worker-debug.js:275:18)
13:09:51         at Module._compile (internal/modules/cjs/loader.js:779:30)
13:09:51         at Object.Module._extensions..js (internal/modules/cjs/loader.js:790:10)
13:09:51         at Module.load (internal/modules/cjs/loader.js:642:32)
13:09:51         at Function.Module._load (internal/modules/cjs/loader.js:555:12)
13:09:51         at Function.Module.runMain (internal/modules/cjs/loader.js:842:10)
13:09:51         at internal/main/run_main_module.js:17:11
13:09:51   ...
12:25:32 not ok 2186 parallel/test-worker-debug
12:25:32   ---
12:25:32   duration_ms: 1.343
12:25:32   severity: fail
12:25:32   exitcode: 1
12:25:32   stack: |-
12:25:32     Test basic debug scenario
12:25:32     This is a message from a worker
12:25:32     Test disabling attach to workers
12:25:32     This is a message from a worker
12:25:32     Test disabled waitForDebuggerOnStart
12:25:32     Test attach to a running worker and then start a new one
12:25:32     This is a message from a worker
12:25:32     Test NodeRuntime.waitForDisconnect in worker
12:25:32     Mismatched noop function calls. Expected exactly 1, actual 0.
12:25:32         at Object.mustCall (/home/iojs/build/workspace/node-test-commit-linux-containered/test/common/index.js:340:10)
12:25:32         at Object.<anonymous> (/home/iojs/build/workspace/node-test-commit-linux-containered/test/parallel/test-worker-debug.js:275:18)
12:25:32         at Module._compile (internal/modules/cjs/loader.js:779:30)
12:25:32         at Object.Module._extensions..js (internal/modules/cjs/loader.js:790:10)
12:25:32         at Module.load (internal/modules/cjs/loader.js:642:32)
12:25:32         at Function.Module._load (internal/modules/cjs/loader.js:555:12)
12:25:32         at Function.Module.runMain (internal/modules/cjs/loader.js:842:10)
12:25:32         at internal/main/run_main_module.js:17:11
12:25:32   ...