This fixes a TypeError in python 3, e.g, when executing uobjnew

Traceback (most recent call last):
  File "./uobjnew", line 134, in <module>
    bpf = BPF(text=program, usdt_contexts=[usdt])
  File "/usr/lib/python3.5/site-packages/bcc/__init__.py", line 224, in __init__
    text = usdt_text + text
TypeError: can't concat bytes to str