TST: Ignore convolution test warnings - #7983

=============================== warnings summary ===============================
astropy/convolution/tests/test_convolve.py::TestConvolve1D::()::test_list
  .../importlib/_bootstrap.py:219: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
    return f(*args, **kwds)

astropy/convolution/tests/test_convolve.py::test_astropy_convolution_against_scipy
  .../importlib/_bootstrap.py:219: ImportWarning: can't resolve package from __spec__ or __package__, falling back on __name__ and __path__
    return f(*args, **kwds)

docs/convolution/kernels.rst
  .../re.py:212: FutureWarning: split() requires a non-empty pattern match.
    return _compile(pattern, flags).split(string, maxsplit)

-- Docs: http://doc.pytest.org/en/latest/warnings.html
======= 1078 passed, 2 skipped, 14 xfailed, 3 warnings in 10.65 seconds ========