Test test_smb_mount_and_access_by_different_users was failing with message
```
kdestroy: Permission denied while initializing krb5
```
This happened because the previous test
`test_smb_access_for_ad_user_at_ipa_client` was calling the fixture
`enable_smb_client_dns_lookup_kdc` which was doing backup of krb5.conf
in a wrong way:
- mktemp (to create a temp file)
- cp /etc/krb5.conf to the temp file
- ...
- mv tempfile /etc/krb5.conf
This flow looses the file permissions, because mktemp creates a file
using the default umask, which results in -rw------- permissions.
The copy does not modify the permissions, and the mv keeps the
permissions from the source => /etc/krb5.conf now has -rw-------.
Fixes: https://pagure.io/freeipa/issue/8115
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
c2b230ce64