Fix some Python 3 goofs and make sure the tests execute with the correct
version of Python (the same the runners themselves were executed with).
diff --git a/elftools/common/utils.py b/elftools/common/utils.py
index 2daed04..7bd1d5b 100644
--- a/elftools/common/utils.py
+++ b/elftools/common/utils.py
@@ -41,6 +41,8 @@
         If stream_pos is provided, the stream is seeked to this position before
         the parsing is done. Otherwise, the current position of the stream is
         used.
+        Note: a bytes object is returned here, because this is what's read from
+        the binary file.
     """
     if stream_pos is not None:
         stream.seek(stream_pos)