ipatests: add missing tests for test_installation.py
    
    Some tests were missing in the nightly:
    - test_installation.py::TestInstallWithCA_DNS3
    - test_installation.py::TestInstallWithCA_DNS4
    
    Relates to https://pagure.io/freeipa/issue/7743
    
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>