ipatests: add KRB5_TRACE to kinit in test_adtrust_install.py
The test test_adtrust_install.py::TestIpaAdTrustInstall::test_add_agent_not_allowed
sometimes fails at kinit in create_active_user:
```
kinit: Password has expired while getting initial credentials
```
Use krb5_trace to catch the required debug information.
Related-to: https://pagure.io/freeipa/issue/8353
Related-to: https://pagure.io/freeipa/issue/8271
Signed-off-by: François Cami <fcami@redhat.com>
Reviewed-By: Michal Polovka <mpolovka@redhat.com>
Reviewed-By: Robbie Harwood <rharwood@redhat.com>