storage: Add duplicate host check for Sheepdog pool def

Check the proposed pool source host XML definition against existing sheepdog
pools to ensure the incoming definition doesn't use the same source host XML
definition as an existing pool.

src/conf/storage_conf.c

@@ -2544,9 +2544,13 @@ virStoragePoolSourceFindDuplicate(virConnectPtr conn,
         case VIR_STORAGE_POOL_DISK:
             matchpool = virStoragePoolSourceFindDuplicateDevices(pool, def);
             break;
+        case VIR_STORAGE_POOL_SHEEPDOG:
+            if (virStoragePoolSourceMatchSingleHost(&pool->def->source,
+                                                    &def->source))
+                matchpool = pool;
+            break;
         case VIR_STORAGE_POOL_MPATH:
         case VIR_STORAGE_POOL_RBD:
-        case VIR_STORAGE_POOL_SHEEPDOG:
         case VIR_STORAGE_POOL_GLUSTER:
         case VIR_STORAGE_POOL_ZFS:
         case VIR_STORAGE_POOL_LAST: