Intermittent buildbot failure and timeout on Android aarch64

[mhsmith]

Bug report

Happened twice in the last two days:

• https://buildbot.python.org/#/builders/1594/builds/84
• https://buildbot.python.org/#/builders/1594/builds/110

In both cases, the sequence of events is:

• TestAndroidOutput.test_bytes fails due to not finding the test start marker line in the logcat. A "threading._dangling was modified" warning is also shown.
• The test passes on the second attempt, so the overall result is success.
• But the end of the test run is not detected, so the worker times out after "1800 seconds without output".