Fix log-reader for Python3 (#3580)

* Fix log-reader for Python3

Signed-off-by: thinker0 <thinker0@linecorp.com>

* typo

Signed-off-by: thinker0 <thinker0@linecorp.com>

* Revert commit

Co-authored-by: thinker0 <thinker0@linecorp.com>

Author: thinker0

heron/shell/src/python/utils.py

@@ -135,15 +135,16 @@ def read_chunk(filename, offset=-1, length=-1, escape_data=False):
   if length == -1:
     length = fstat.st_size - offset
 
-  with open(filename, "r") as fp:
+  with open(filename, "rb") as fp:
     fp.seek(offset)
     try:
       data = fp.read(length)
     except IOError:
       return {}
 
   if data:
-    data = _escape_data(data) if escape_data else data
+    # use permissive decoding and escaping if escape_data is set, otherwise use strict decoding
+    data = _escape_data(data) if escape_data else data.decode()
     return dict(offset=offset, length=len(data), data=data)
 
   return dict(offset=offset, length=0)