storage: Add duplicate source pool for Gluster pool def

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

src/conf/storage_conf.c

@@ -2464,6 +2464,7 @@ virStoragePoolSourceFindDuplicate(virConnectPtr conn,
                 matchpool = pool;
             break;
         case VIR_STORAGE_POOL_NETFS:
+        case VIR_STORAGE_POOL_GLUSTER:
             if (STREQ(pool->def->source.dir, def->source.dir) &&
                 virStoragePoolSourceMatchSingleHost(&pool->def->source,
                                                     &def->source))
@@ -2551,7 +2552,6 @@ virStoragePoolSourceFindDuplicate(virConnectPtr conn,
             break;
         case VIR_STORAGE_POOL_MPATH:
         case VIR_STORAGE_POOL_RBD:
-        case VIR_STORAGE_POOL_GLUSTER:
         case VIR_STORAGE_POOL_ZFS:
         case VIR_STORAGE_POOL_LAST:
             break;