detach_spawn failing flakily on travis

The detach_spawn test from #2600 (closed) and #2601 (closed) just failed once on travis:

https://travis-ci.org/DynamoRIO/dynamorio/jobs/300006348

281/281 Test #265: code_api|api.detach_spawn ........................................***Failed  Required regular expression not found.Regex=[^\.*all done
$
] 90.50 sec
..........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................<ERROR: master_signal_handler with no siginfo (i#26?): tid=20526, sig=12>
......................................Timeout after 90 seconds