[SSSD] [sssd PR#365][opened] PYTHON: Define constants as bytes instead of strings

[fidencio]

   URL: https://github.com/SSSD/sssd/pull/365
Author: fidencio
 Title: #365: PYTHON: Define constants as bytes instead of strings
Action: opened

PR body:
"""
When using python3 getsidbyname() and getnamebysid() expect the key as
bytes instead of strings, and currently those are defined as strings.
So, in order to avoid people working around this by doing
`pysss_nss_idmap.SID_KEY.encode('utf-8')` let's make their life easier
and properly have those constants defined as bytes.

Resolves: https://pagure.io/SSSD/sssd/issue/3491

Signed-off-by: Fabiano Fidêncio <fidencio(a)redhat.com&gt;
"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/365/head:pr365
git checkout pr365