ipatests: test_installation: add install test scenarios
    
    test_hostname_parameter: Test for issue 2692 ipa-server-install ignores --hostname:
    check whether hostname provided in `--hostname` parameter is being taken into account and set as new hostname without prompting for it again
    
    test_ad_subpackage_dependency: Test for issue 4011 ipa-server-install crashes when AD subpackage is not installed:
    test if ipa-server installation succeeds without `freeipa-ipa-server-trust-ad` installed
    
    test_backup_of_cs_cfg_should_be_created: Test for issue 4166 Backup CS.cfg before modifying it:
    test if ipa-server installer backs up CS.cfg before modifying it
    
    test_installer_wizard_should_prompt_for_DNS: Test for issue 2575 [RFE] Installer wizard should prompt for DNS:
    test if installer is asking for DNS setup details if not provided as parameter
    
    Related: https://pagure.io/freeipa/issue/2692
    Related: https://pagure.io/freeipa/issue/4011
    Related: https://pagure.io/freeipa/issue/4166
    Related: https://pagure.io/freeipa/issue/2575
    
    Signed-off-by: Michal Polovka <mpolovka@redhat.com>
    Reviewed-By: Michal Polovka <mpolovka@redhat.com>
    Reviewed-By: Sergey Orlov <sorlov@redhat.com>
    Reviewed-By: Rob Crittenden <rcritten@redhat.com>