Brocade: Fix lookup UnboundLocalError

If we get an exception when getting the southbound client in method
get_device_mapping_from_network we will end up seeing the following
error:

  UnboundLocalError: local variable 'conn' referenced before assignment

This patch fixes this issue by making sure that the conn variable exists
even if that call fails.

TrivialFix
Closes-Bug: #1888550
Change-Id: I621a00d34e9c2b14234e11e94857a39fe54a111f

cinder/tests/unit/zonemanager/test_brcd_fc_san_lookup_service.py

@@ -124,6 +124,16 @@ class TestBrcdFCSanLookupService(brcd_lookup.BrcdFCSanLookupService,
             initiator_list, target_list)
         self.assertDictEqual(_device_map_to_verify, device_map)
 
+    @mock.patch.object(brcd_lookup.BrcdFCSanLookupService,
+                       '_get_southbound_client', side_effect=ValueError)
+    def test_get_device_mapping_from_network_fail(self,
+                                                  get_southbound_client_mock):
+        initiator_list = [parsed_switch_port_wwns[1]]
+        target_list = [parsed_switch_port_wwns[0], '20240002ac000a40']
+        self.assertRaises(brcd_lookup.exception.FCSanLookupServiceException,
+                          self.get_device_mapping_from_network,
+                          initiator_list, target_list)
+
 
 class FakeClient(object):
     def is_supported_firmware(self):

cinder/zonemanager/drivers/brocade/brcd_fc_san_lookup_service.py

@@ -111,6 +111,7 @@ class BrcdFCSanLookupService(fc_service.FCSanLookupService):
                 # Get name server data from fabric and find the targets
                 # logged in
                 nsinfo = ''
+                conn = None
                 try:
                     LOG.debug("Getting name server data for "
                               "fabric %s", fabric_ip)

releasenotes/notes/brocade_looup_fail_get_client-179151d449a34aa4.yaml

@@ -0,0 +1,5 @@
+---
+fixes:
+  - |
+    Fix `UnboundLocalError` on the Brocade lookup driver on southbound client
+    creation failure during the device mapping retrieval (Bug #1888550).