Title: #850: sudo: use proper datetime for default modifyTimestamp value
The current default was simply "1", however OpenLDAP server was unable
to compare modifyTimestamp attribute to simple number. A proper datetime
is required by OpenLDAP.
It worked correctly on 389-ds.
Steps to reproduce:
1. install openldap server
2. run sssd
3. there are no sudo rules on the server and there are no cached objects
4. you'll see in the logs that sudo smart refresh uses
`(&(&(objectclass=sudoRole)(modifyTimestamp>=1))...` filter (`1` instead of
proper datetime value)
To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/850/head:pr850
git checkout pr850