Title: #602: Handle e-mail addresses that conflict with FQDNs
These patches address ticket https://pagure.io/SSSD/sssd/issue/3607
reverting two patches and add a test to make sure sssd now behaves as it should.
To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/602/head:pr602
git checkout pr602