Description of problem:

When killsnoop output traces, TypeError happens.


Version-Release number of selected component (if applicable):

# rpm -qa|grep bcc
bcc-tools-0.7.0-2.fc28.x86_64
bcc-0.7.0-2.fc28.x86_64
python3-bcc-0.7.0-2.fc28.x86_64


How reproducible:

Always


Steps to Reproduce:
1. $ sudo /usr/share/bcc/tools/killsnoop
2. open new terminal emulator 

Actual results:

$ sudo /usr/share/bcc/tools/killsnoop
TIME      PID    COMM             SIG  TPID   RESULT



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 "./killsnoop", line 143, in print_event
    event.pid, event.comm, event.sig, event.tpid, event.ret))
TypeError: %b requires a bytes-like object, or an object that implements __bytes__, not 'str'
(and this traceback repeats)


Additional info:

This case is a similar case of #1636293

    printb(b"%-9s %-6d %-16s %-4d %-6d %d" % (strftime("%H:%M:%S"),
        event.pid, event.comm, event.sig, event.tpid, event.ret))

b"%-9s" needs a binary object, but strftime returns a string object.

Thanks,