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ARROW-1054: [Python] Fix test failure on pandas 0.19.2, some refactoring

For esoteric reasons, `MultiIndex.from_arrays` rejects non-writeable NumPy arrays. This problem isn't present in pandas 0.20.1

Author: Wes McKinney <wes.mckinney@twosigma.com>

Closes #705 from wesm/ARROW-1054 and squashes the following commits:

f7dfbb24 [Wes McKinney] Factor out table to blocks into pandas_compat, fix pandas 0.19.2 test failure