ipatests: fix CA less expectations
The test TestServerInstall::test_ca_2_certs has a
wrong expectation. Scenario:
install a CA-less master with
ipa-server-install --ca-cert-file root.pem
where root.pem contains the CA that signed the http and ldap
certificates + an additional (unneeded) CA cert.
The test was expecting a failure, but this scenario is not
problematic as long as the unneeded CA cert is not added.
Related to https://pagure.io/freeipa/issue/6289 which has been
closed as won't fix
Reviewed-By: Fraser Tweedale <ftweedal@redhat.com>