python: Add compatability helpers to determine if type is really bytes

python: Add compatability helpers to determine if type is really bytes

py3compat has PyBytes_Check macro which evalates to PyString_Check in
python2. To help switch behaviour based on whether you are dealing
with the bytes type the following macros have been added.

IsPy3Bytes
IsPy3BytesOrString

IsPy3Bytes will evaluate to false in python2 and will return the
expected result in python3. IsPy3BytesOrString will test for string
type alone in python2 or bytes and string in python3.

Signed-off-by: Noel Power <noel.power@suse.com>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>