run_tests.py hangs in process or control.controller

Oddly enough it seems to happen less often with -v.

Excerpt from one of the hangs when using -v:

======================================================================
               test.integ.installation.TestInstallation               
======================================================================

test_install                                           0 ms  [SUCCESS]
test_sdist                                           627 ms  [SUCCESS]

----------------------------------------------------------------------
Ran 2 tests in 0.628s

OK

======================================================================
                    test.integ.process.TestProcess                    
======================================================================

During the hang I see the following tor and python processes:

tlyu      96853  1.4  9.0 21474964912 365204 pts/0 S+ 15:39   0:01 /home/tlyu/src/stem/../tor/src/or/tor -f /home/tlyu/src/stem/test/data/torrc __OwningControllerProcess 96673
tlyu      96673  4.4  1.0 394728 41408 pts/0    S+   15:39   0:05 python ./run_tests.py --tor ../tor/src/or/tor --all --log notice --target RUN_AL  -v
tlyu      96680  1.2  0.0      0     0 pts/0    ZN+  15:39   0:01 [python] <defunct>
tlyu      96686  0.0  0.0      0     0 pts/0    ZN+  15:39   0:00 [python] <defunct>
tlyu      96687  0.0  0.0      0     0 pts/0    ZN+  15:39   0:00 [python] <defunct>
tlyu      96689  0.0  0.0      0     0 pts/0    ZN+  15:39   0:00 [python] <defunct>
tlyu      96690  0.0  0.0      0     0 pts/0    ZN+  15:39   0:00 [python] <defunct>
tlyu      96692  0.0  0.0      0     0 pts/0    ZN+  15:39   0:00 [python] <defunct>
tlyu      96693  0.0  0.0      0     0 pts/0    ZN+  15:39   0:00 [python] <defunct>
tlyu      96701  0.0  0.0      0     0 pts/0    ZN+  15:39   0:00 [python] <defunct>
tlyu      96702  0.0  0.0      0     0 pts/0    ZN+  15:39   0:00 [python] <defunct>