[CI] CI failing for python Xcode 7.3

The last couple of PR triggered builds have failed with this :

CMake Error at cmake_modules/FindNumPy.cmake:62 (message):
NumPy import failure:
Traceback (most recent call last):
File "<string>", line 1, in <module>
File "/Users/travis/build/apache/arrow/pyarrow-test-2.7/lib/python2.7/site-packages/numpy/_init_.py", line 142, in <module>
from . import add_newdocs
File "/Users/travis/build/apache/arrow/pyarrow-test-2.7/lib/python2.7/site-packages/numpy/add_newdocs.py", line 13, in <module>
from numpy.lib import add_newdoc
File "/Users/travis/build/apache/arrow/pyarrow-test-2.7/lib/python2.7/site-packages/numpy/lib/_init_.py", line 8, in <module>
from .type_check import *
File "/Users/travis/build/apache/arrow/pyarrow-test-2.7/lib/python2.7/site-packages/numpy/lib/type_check.py", line 11, in <module>
import numpy.core.numeric as _nx
File "/Users/travis/build/apache/arrow/pyarrow-test-2.7/lib/python2.7/site-packages/numpy/core/_init_.py", line 26, in <module>
raise ImportError(msg)

https://travis-ci.org/apache/arrow/jobs/489917808