Adding test-cases for ipa-cacert-manage
    
        File     :  ipatests/test_integration/test_external_ca.py
    
        Scenario1:  Manual renew external CA cert with invalid file
                    when ipa-server is installed with external-ca
                    and renew with invalid cert file the renewal
                    should fail.
    
        Scenario2:  install CA cert manually
                    Install ipa-server. Create rootCA, using
                    ipa-cacert-manage install option install
                    new cert from RootCA
    
    Signed-off-by: Anuja More <amore@redhat.com>
    
    Signed-off-by: Anuja More <amore@redhat.com>
    Reviewed-By: Christian Heimes <cheimes@redhat.com>