Bug#992673: libgpuarray: autopkgtest depends on libclblas-dev which is not in testing *and* has skip-not-installable

[Rebecca N. Palmer]

clblas has been replaced by clblast, so I tried switching to that, but 
doing so makes a varying number of cases of test_gemv fail, e.g.

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FAIL: pygpu.tests.test_blas.test_gemv((128, 50), 'float32', 'c', True, 
False, 2, True, False)
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Traceback (most recent call last):
   File "/usr/lib/python3/dist-packages/nose/case.py", line 197, in runTest
     self.test(*self.arg)
   File "/usr/lib/python3/dist-packages/pygpu/tests/test_blas.py", line 
22, in f
     func(*args, **kwargs)
   File "/usr/lib/python3/dist-packages/pygpu/tests/test_blas.py", line 
106, in gemv
     numpy.testing.assert_allclose(cr, numpy.asarray(gr), rtol=1e-6)
   File 
"/usr/lib/python3/dist-packages/numpy/testing/_private/utils.py", line 
1527, in assert_allclose
     assert_array_compare(compare, actual, desired, err_msg=str(err_msg),
   File 
"/usr/lib/python3/dist-packages/numpy/testing/_private/utils.py", line 
764, in assert_array_compare
     flagged = func_assert_same_pos(x, y, func=isnan, hasval='nan')
   File 
"/usr/lib/python3/dist-packages/numpy/testing/_private/utils.py", line 
740, in func_assert_same_pos
     raise AssertionError(msg)
AssertionError:
Not equal to tolerance rtol=1e-06, atol=0

x and y nan location mismatch:
  x: array([2978.7732, 2797.7976, 2703.4192, 3382.4128, 2927.2117, 
3026.7405,
        3039.3098, 3189.797 , 2808.6248, 3314.7722, 3276.5303, 2989.4634,
        2783.26  , 3235.359 , 3226.2778, 3100.7969, 3069.6052, 3033.824 ,...
  y: array([2978.7732, 2797.7976, 2703.4192, 3382.4128, 2927.2117, 
3026.7405,
        3039.3098, 3189.797 , 2808.6248, 3314.7722, 3276.5303, 2989.4634,
        2783.26  , 3235.359 ,       nan, 3100.7969, 3069.6052, 3033.824 ,...

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