keytab.py python 3.x support

[jpalko]

I tried running this with a python 3.6 virtualenv on a CentOS 7 system having python 2.7 and 3.6 installed.

I ran into the problem with updating a previously made ktutil keytab file that using this code ended with:

(keytab) [user@host ~]$ python keytab.py --update user --domain=REALM --keytab=user.keytab 
Traceback (most recent call last):
  File "keytab.py", line 110, in <module>
    wait()
  File "keytab.py", line 101, in wait
    lines = child.before.strip().split('\n').decode()
TypeError: a bytes-like object is required, not 'str'

I modified line 101 from
lines = child.before.strip().split('\n')
to
lines = child.before.strip().decode().split('\n')
which helped the code to work.

Anyway, this little bit of python was helpful for myself, so thanks. :)

[Tagar]

Thanks for letting me know. Feel free to submit a PR