[GPU-Plugin] Major refactor 2 (#2664)

* Change cmake option

* Move source files

* Move google tests

* Move python tests

* Move benchmarks

* Move documentation

* Remove makefile support

* Fix test run

* Move GPU tests

tests/python-gpu/test_gpu_prediction.py

@@ -0,0 +1,37 @@
+from __future__ import print_function
+#pylint: skip-file
+import xgboost as xgb
+import testing as tm
+import numpy as np
+import unittest
+from nose.plugins.attrib import attr
+
+rng = np.random.RandomState(1994)
+
+@attr('gpu')
+class TestGPUPredict (unittest.TestCase):
+    def test_predict(self):
+        iterations = 1
+        np.random.seed(1)
+        test_num_rows = [10,1000,5000]
+        test_num_cols = [10,50,500]
+        for num_rows in test_num_rows:
+            for num_cols in test_num_cols:
+                dm = xgb.DMatrix(np.random.randn(num_rows, num_cols), label=[0, 1] * int(num_rows/2))
+                watchlist = [(dm, 'train')]
+                res = {}
+                param = {
+                    "objective":"binary:logistic",
+                    "predictor":"gpu_predictor",
+                    'eval_metric': 'auc',
+                }
+                bst = xgb.train(param, dm,iterations,evals=watchlist, evals_result=res)
+                assert self.non_decreasing(res["train"]["auc"])
+                gpu_pred = bst.predict(dm, output_margin=True)
+                bst.set_param({"predictor":"cpu_predictor"})
+                cpu_pred = bst.predict(dm, output_margin=True)
+                np.testing.assert_allclose(cpu_pred, gpu_pred, rtol=1e-5)
+
+    def non_decreasing(self, L):
+        return all((x - y) < 0.001 for x, y in zip(L, L[1:]))
+