Fix data decode for watch/watch.py:49

[dbazhal]

There is error like

UnicodeDecodeError: 'utf-8' codec can't decode byte 0xd0 in position 2047: unexpected end of data
<...>
  File "kubernetes/watch/watch.py", line 134, in stream
    for line in iter_resp_lines(resp):
  File "kubernetes/watch/watch.py", line 49, in iter_resp_lines
    seg = seg.decode('utf8')

So this PR fixes that. Related somehow to #104

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[dbazhal]

/assign roycaihw

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[dbazhal]

Much sorry, messed up with commit author and git history... Will recreate this PR again.