The following three tools are recently changed to use
printb in order to flush out the result.
  opensnoop.py, tcpaccept.py, tcpconnect.py

With python3, however, these tools have errors like below:
  TypeError: %b requires a bytes-like object, or an object that implements __bytes__, not 'str'
  Traceback (most recent call last):
    File "_ctypes/callbacks.c", line 234, in 'calling callback function'
    File "/usr/lib/python3.6/site-packages/bcc/table.py", line 572, in raw_cb_
      callback(cpu, data, size)
    File "../../tools/opensnoop.py", line 248, in print_event
      printb(b'%s' % event.fname.decode('utf-8', 'replace'))

This patch fixed printb related issues for these three tools
for python3. The python2 still works with the fix.
Signed-off-by: Yonghong Song <yhs@fb.com>