On Python 2, shlex.split() raises if you pass it a unicode object with
non-ASCII characters in it.  The Ansible codebase copes by explicitly
converting the string using to_bytes() before passing it to
shlex.split().

On Python 3, shlex.split() raises ('bytes' object has no attribute 'read')
if you pass a bytes object.  Oops.

This commit introduces a new wrapper function, shlex_split, that
transparently performs the to_bytes/to_unicode conversions only on
Python 2.

Currently I've only converted one call site (the one that was causing a
unit test to fail on Python 3).  If this approach is deemed suitable,
I'll convert them all.