So, finally got to a Fedora21 beta to try this out today; the immediate problem, as identified by Joe Julian, is the shutdown() call in the __del__ method of Rados.  

Presumably something about object destructors is clashing with starting new threads; the hang occurs with a gdb backtrace like so:

1710 in sem_wait () from /lib64/libpthread.so.0
#1  0x00007fad36fbce75 in PyThread_acquire_lock ()
   from /lib64/libpython2.7.so.1.0
#2  0x00007fad36fc0c82 in lock_PyThread_acquire_lock ()
   from /lib64/libpython2.7.so.1.0
#3  0x00007fad36f91ade in PyEval_EvalFrameEx () from /lib64/libpython2.7.so.1.0
#4  0x00007fad36f92490 in PyEval_EvalCodeEx () from /lib64/libpython2.7.so.1.0
#5  0x00007fad36f90b74 in PyEval_EvalFrameEx () from /lib64/libpython2.7.so.1.0
#6  0x00007fad36f92490 in PyEval_EvalCodeEx () from /lib64/libpython2.7.so.1.0
#7  0x00007fad36f90b74 in PyEval_EvalFrameEx () from /lib64/libpython2.7.so.1.0
#8  0x00007fad36f90c76 in PyEval_EvalFrameEx () from /lib64/libpython2.7.so.1.0
#9  0x00007fad36f92490 in PyEval_EvalCodeEx () from /lib64/libpython2.7.so.1.0
#10 0x00007fad36f90b74 in PyEval_EvalFrameEx () from /lib64/libpython2.7.so.1.0
#11 0x00007fad36f90c76 in PyEval_EvalFrameEx () from /lib64/libpython2.7.so.1.0
#12 0x00007fad36f92490 in PyEval_EvalCodeEx () from /lib64/libpython2.7.so.1.0
#13 0x00007fad36f1e6dc in function_call () from /lib64/libpython2.7.so.1.0
#14 0x00007fad36ef98d3 in PyObject_Call () from /lib64/libpython2.7.so.1.0
#15 0x00007fad36f087e5 in instancemethod_call ()
   from /lib64/libpython2.7.so.1.0
#16 0x00007fad36ef98d3 in PyObject_Call () from /lib64/libpython2.7.so.1.0
#17 0x00007fad36f8b557 in PyEval_CallObjectWithKeywords ()
   from /lib64/libpython2.7.so.1.0
#18 0x00007fad36f5082c in slot_tp_del () from /lib64/libpython2.7.so.1.0
#19 0x00007fad36f4b88a in subtype_dealloc () from /lib64/libpython2.7.so.1.0
#20 0x00007fad36f2e1ff in insertdict_by_entry ()
   from /lib64/libpython2.7.so.1.0
#21 0x00007fad36f2fcc0 in dict_set_item_by_hash_or_entry ()
   from /lib64/libpython2.7.so.1.0
#22 0x00007fad36f3467c in _PyModule_Clear () from /lib64/libpython2.7.so.1.0
#23 0x00007fad36fa1c5b in PyImport_Cleanup () from /lib64/libpython2.7.so.1.0
#24 0x00007fad36fad598 in Py_Finalize () from /lib64/libpython2.7.so.1.0
#25 0x00007fad36faced8 in Py_Exit () from /lib64/libpython2.7.so.1.0
#26 0x00007fad36fad01a in handle_system_exit.part ()
   from /lib64/libpython2.7.so.1.0
#27 0x00007fad36fad29d in PyErr_PrintEx () from /lib64/libpython2.7.so.1.0
#28 0x00007fad36fadea3 in PyRun_SimpleFileExFlags ()
   from /lib64/libpython2.7.so.1.0
#29 0x00007fad36fbf30a in Py_Main () from /lib64/libpython2.7.so.1.0
#30 0x00007fad361e6fe0 in __libc_start_main () from /lib64/libc.so.6
#31 0x000000000040071e in _start ()

I'm guessing something about the changed shutdown is causing the deadlock?...  Anyway, I'm pretty sure we can afford to remove that __del__ method, and that's another easily-applied workaround for the field.