Propagate attributes down the Test tree

[anshooarora]

The current behavior does not propagate top-level attributes down the attribute tree.

Example:

extent.createTest("Test").assignCategory("tag")
  .createNode("Node");

In the above example, Test will have tag category but Node will not. This is technically not correct since all parent tags must also be assigned to children. Fix would be to propagate all added attributes down the test graph.