ipatests: update tests for ipa-server-certinstall

The test test_http_intermediate_ca was expecting success when
it should expect a failure. Scenario:
- install IPA ca-less with certs signed by rootCA
- call ipa-server-certinstall with a cert signed by a subCA
to replace http cert.
In this case, the command should refust changing the cert
(otherwise the clients won't be able any more to use
ipa * commands as the subca is not installed in /etc/ipa/nssdb
or in /etc/ipa/ca.crt).

The commit fixes the test expectation and marks the test as
xfail (see ticket 7759).

The test test_ds_intermediate_ca was expecting success when
it should expect a failure. Same scenario as above, but for
the ldap server cert.

The commit fixes the test expectation and removes the xfail
(ticket 6959 was closed as invalid).

Note:
The behavior differs for ldap and http cert because LDAP server
is using a NSSDB and http server is using openssl, hence
ipa-server-certinstall follows 2 different code paths when
changing the server cert.

Related to https://pagure.io/freeipa/issue/7759
Related to https://pagure.io/freeipa/issue/6959

Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>

ipatests/test_integration/test_caless.py

@@ -1452,18 +1452,24 @@ class TestCertInstall(CALessBase):
 
         assert result.returncode > 0
 
+    @pytest.mark.xfail(reason='freeipa ticket 7759', strict=True)
     def test_http_intermediate_ca(self):
         "Install new HTTP certificate issued by intermediate CA"
 
         result = self.certinstall('w', 'ca1/subca/server')
-        assert result.returncode == 0, result.stderr_text
+        # As the intermediate CA is not trusted, command must fail
+        assert_error(result,
+                     "Peer's certificate issuer is not trusted")
 
-    @pytest.mark.xfail(reason='freeipa ticket 6959', strict=True)
     def test_ds_intermediate_ca(self):
         "Install new DS certificate issued by intermediate CA"
 
         result = self.certinstall('d', 'ca1/subca/server')
-        assert result.returncode == 0, result.stderr_text
+        # As the intermediate CA is not trusted, command must fail
+        assert_error(result,
+                     "Peer's certificate issuer is not trusted "
+                     "(certutil: certificate is invalid: Peer's Certificate "
+                     "issuer is not recognized.")
 
     def test_self_signed(self):
         "Install new self-signed certificate"