Skip onnx test if onnxruntime not found. (#2099)

Author: benson31

ci_test/integration_tests/test_integration_onnx_output.py

@@ -15,7 +15,12 @@
 onnx_model = current_dir + '/experiments/test_integration_onnx_output/lbann.onnx'
 import tools
 import data.mnist
-import onnxruntime
+
+try:
+    import onnxruntime
+except ModuleNotFoundError:
+    pytest.skip("Skipping ONNX runtime test; onnxruntime not found.",
+                allow_module_level=True)
 
 # ==============================================
 # Options