[SSSD] [sssd PR#868][opened] ifp: let cache_req parse input name so it can fallback to upn search

[pbrezina]

   URL: https://github.com/SSSD/sssd/pull/868
Author: pbrezina
 Title: #868: ifp: let cache_req parse input name so it can fallback to upn search
Action: opened

PR body:
"""
UPN search expects that the input name is in its fully qualified form.
However, GetUserAttr calls cache_req with unqualified username therefore
it never fallback to UPN search.

Steps to reproduce:
1. Configure SSSD against AD
2. Set UPN to `TestUserUPN(a)ad.vm`
3. Run:

```
dbus-send --print-reply --system --dest=org.freedesktop.sssd.infopipe
/org/freedesktop/sssd/infopipe org.freedesktop.sssd.infopipe.GetUserAttr
string:[e-mail] array:string:name
Error sbus.Error.NotFound: No such file or directory
```

Resolves:
https://pagure.io/SSSD/sssd/issue/4065
"""

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/868/head:pr868
git checkout pr868