message: Add unit test for K.all
diff: @@ -589,6 +589,21 @@ class TestBackendOps(unittest.TestCase):
  x / c,
  c / x,
  ]
  + @compareForwardExact()
  + def testAll(self, b):
  + return b.all(b.variable(m(3, 3)))
  +
  + @compareForwardExact()
  + def testAllKeepdims(self, b):
  + return b.all(b.variable(m(3, 3)), keepdims=True)
  +
  + @compareForwardExact()
  + def testAllAxis(self, b):
  + return b.all(b.variable(m(2, 3, 4, 5)), axis=[1, 3])
  +
  + @compareForwardExact()
  + def testAllNegAxis(self, b):
  + return b.all(b.variable(m(3, 4, 5)), axis=-1)
  @opTest([
  [m(3, 3)],
  