ipatests: mark known failures as xfail
    
    The tests in test_integration/test_installation.py
    that inherit from InstallTestBase2 all fail in
    test_replica2_ipa_kra_install because of ticket
    7654: ipa-kra-install fails on DL1
    
    This is an issue linked to dogtag (see
    https://pagure.io/dogtagpki/issue/3055), where the
    installation of a KRA clone creates a range depletion
    when multiple clones are created from the same master.
    
    Marking the tests as known failure, waiting for dogtag's
    fix.
    
    Related to https://pagure.io/freeipa/issue/7654
    
    Reviewed-By: Christian Heimes <cheimes@redhat.com>