_ExportQuery: Use node allocation lock

Block instance allocations when all node locks will be acquired.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

lib/cmdlib.py

@@ -13951,6 +13951,9 @@ class _ExportQuery(_QueryBase):
         locking.LEVEL_NODE: self.wanted,
         }
+      if not self.names:
+        lu.needed_locks[locking.LEVEL_NODE_ALLOC] = locking.ALL_SET
+
   def DeclareLocks(self, lu, level):
     pass