Fix tempest case "test_delete_ss_from_sn_used_by_share_server"

The case use fake data in security service, which may cause backend driver
fail.
Refer to the case "test_try_update_valid_keys_sh_server_exists", just ignore
the error of the backend driver procedure.

Change-Id: I783652486fcf92b543c0a620409c9e41d33cab56
Closes-Bug: #1531758
diff --git a/manila_tempest_tests/tests/api/test_security_services_mapping_negative.py b/manila_tempest_tests/tests/api/test_security_services_mapping_negative.py
index de0064c..834deb5 100644
--- a/manila_tempest_tests/tests/api/test_security_services_mapping_negative.py
+++ b/manila_tempest_tests/tests/api/test_security_services_mapping_negative.py
@@ -13,6 +13,8 @@
 #    License for the specific language governing permissions and limitations
 #    under the License.
 
+from oslo_log import log  # noqa
+import six  # noqa
 from tempest import config  # noqa
 from tempest import test  # noqa
 from tempest_lib import exceptions as lib_exc  # noqa
@@ -21,6 +23,7 @@
 from manila_tempest_tests.tests.api import base
 
 CONF = config.CONF
+LOG = log.getLogger(__name__)
 
 
 class SecServicesMappingNegativeTest(base.BaseSharesTest):
@@ -99,8 +102,21 @@
 
         self.shares_client.add_sec_service_to_share_network(
             fresh_sn["id"], self.ss["id"])
-        self.create_share(
-            share_network_id=fresh_sn["id"], cleanup_in_class=False)
+
+        # Security service with fake data is used, so if we use backend driver
+        # that fails on wrong data, we expect error here.
+        # We require any share that uses our share-network.
+        try:
+            self.create_share(
+                share_network_id=fresh_sn["id"], cleanup_in_class=False)
+        except Exception as e:
+            # we do wait for either 'error' or 'available' status because
+            # it is the only available statuses for proper deletion.
+            LOG.warning("Caught exception. It is expected in case backend "
+                        "fails having security-service with improper data "
+                        "that leads to share-server creation error. "
+                        "%s" % six.text_type(e))
+
         self.assertRaises(lib_exc.Forbidden,
                           self.cl.remove_sec_service_from_share_network,
                           fresh_sn["id"],