always use pthread on monkey patched environment

eventlet_threading.py

import eventlet

eventlet.monkey_patch()

if eventlet.patcher.is_monkey_patched("thread"):
    print("Patched")
    threading = eventlet.patcher.original("threading")
else:
    print("Not Patched")
    import threading

print(threading.current_thread.__module__)
# Will print 'threading'
assert threading.current_thread.__module__ == 'threading'
# No error will raised