Add test_create_server_when_memory_quota_is_full to skip list

While we trace root cause on Bug #1818886, we need this test in skip
list as it is failing on gate pipeline.

Change-Id: I9add83a5ef0f3c46835d6bf6944483cb818ad87a
Related-Bug: #1818886

roles/validate-tempest/vars/tempest_skip_master.yml

@@ -8,6 +8,9 @@ known_failures:
   - test: 'tempest.api.network.test_ports.PortsIpV6TestJSON.test_update_port_with_two_security_groups_and_extra_attributes'
     reason: 'Test is failing with SecurityGroupNotFound'
     lp: 'https://bugs.launchpad.net/tripleo/+bug/1818860'
+  - test: 'tempest.api.compute.admin.test_quotas_negative.QuotasAdminNegativeTest.test_create_server_when_memory_quota_is_full'
+    reason: 'Test is failing on unknown API error: nova.exception.GlanceConnectionFailed'
+    lp: 'https://bugs.launchpad.net/tempest/+bug/1818886'
   - test: 'tempest.scenario.test_network_basic_ops.TestNetworkBasicOps.test_port_security_macspoofing_port'
     reason: 'It can be removed when bug for OVN is repaired'
     lp: 'https://bugs.launchpad.net/tempest/+bug/1728886'