fix nightly issues related to onnx dependencies

- Windows OOBE (pip) tests & Linus OOBE tests: skip onnx_model_test. This test requires
onnx to be installed. Skip Until we decide to add onnx dependencies to
OOBE test environment.

Tests/Install/linux/prep-run-test.sh

@@ -21,7 +21,9 @@ which cntk
 MODULE_DIR="\$(python -c "import cntk, os, sys; sys.stdout.write(os.path.dirname(os.path.abspath(cntk.__file__)))")"
 [ \$? -eq 0 ]
 
-[ "\$TEST_DEVICE" = "gpu" ] && pytest "\$MODULE_DIR" --deviceid \$TEST_DEVICE
+# onnx_model_test requires onnx to be installed.
+# Skip this test until we decide to add onnx dependencies to OOBE test environment. 
+[ "\$TEST_DEVICE" = "gpu" ] && pytest "\$MODULE_DIR" --deviceid \$TEST_DEVICE -k "not onnx_model_test"
 # TODO not all (doc) tests run on CPU
 
 # Installation validation example from CNTK.wiki (try from two different paths):

Tests/Install/windows/test-install.bat

@@ -24,7 +24,7 @@ and not combine_test and not evaluation_test and not fp16_test and not free_stat
 and not function_tests and not kernel_test and not linear_test and not non_diff_test and not recurrent_test ^
 and not reshaping_test and not sequence_test and not sparse_test and not stop_gradient_test ^
 and not userfunction_complex_test and not userfunction_test and not random_ops_test and not function_test ^
-and not onnx_format_test and not onnx_op_test and not persist_test and not tensor_test and not value_test ^
+and not onnx_format_test and not onnx_op_test and not onnx_model_test and not persist_test and not tensor_test and not value_test ^
 and not variables_test and not distributed_test and not trainer_test and not training_session and not misc_test
 
 where cntk && ^