Use eager tensor
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Passing `[4, 2]` as `shape` to `array_ops.reshape` always produces an error (in my case with a silent exit and no clue about what happened). Seems to happen because `[4,2]` is of type `List` and when `array_ops.reshape` calls `pywrap_tfe.TFE_Py_FastPathExecute` it expects Eager tensors.

I have tested this in two different scenarios:
 * The first, was working without issues before, in this case because when invoking `pywrap_tfe.TFE_Py_FastPathExecute` it produced a `_core._FallbacException`.
* On the second one, which had more complexity, I am not fully sure why (I guess because the context is different), `pywrap_tfe.TFE_Py_FastPathExecute` simply fails, and doesn't return or throw any error.

After this change, both scenarios work fine.

