Change conv_ops_test_gpu to size large

Author: sunway513

tensorflow/python/kernel_tests/BUILD

@@ -2974,7 +2974,7 @@ cuda_py_test(
 
 cuda_py_test(
     name = "conv_ops_test",
-    size = "medium",
+    size = "large",
     srcs = ["conv_ops_test.py"],
     additional_deps = [
         "//third_party/py/numpy",