test failure in filter_design

[ev-br]

Found in testing @matthew-brett's manylinux wheels (https://mail.scipy.org/pipermail/numpy-discussion/2016-February/074841.html) on python 2.7.11 on a 64-bit ubuntu trusty.

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FAIL: Regression test for #651: better handling of badly conditioned
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Traceback (most recent call last):
  File "/home/br/virtualenvs/manylinux/local/lib/python2.7/site-packages/scipy/signal/tests/test_filter_design.py", line 167, in test_bad_filter
    assert_raises(BadCoefficients, tf2zpk, [1e-15], [1.0, 1.0])
  File "/home/br/virtualenvs/manylinux/local/lib/python2.7/site-packages/numpy/testing/utils.py", line 1109, in assert_raises
    return nose.tools.assert_raises(*args,**kwargs)
AssertionError: BadCoefficients not raised

[rgommers]

Should be fixed by gh-5796

[rgommers]

Will fix this temporarily as part of gh-7336 by skipping the test, it's unreliable. gh-5796 will be the permanent fix.