[DT] Fix #915. Adjust `_setColumns` to deep clone properly and only once on recursive nodes.

Adjust `_setColumns` to deep clone properly and only once on recursive nodes.

`_setColumns` has a local function called `copyObj` that is used to clone the columns config to prevent it from potentially busting the use of that object outside of DataTable. `arrayIndex`, a pointer to `Y.Array.indexOf`, is used to look up to prevent infinite recursion during the clone. 

`arrayIndex` had the arguments in the wrong order. This pr is submitted to correct this.

Fix #915