Show duration of each UT case (#4809)

docs/source/conf.py

@@ -105,6 +105,7 @@ linkcheck_ignore = [
     # Some URLs that often fail
     r'https://www\.cs\.toronto\.edu/',                      # CIFAR-10
     r'https://help\.aliyun\.com/document_detail/\d+\.html', # Aliyun
+    r'http://www\.image-net\.org/',                         # ImageNet
 ]
 
 # Ignore all links located in release.rst

test/pytest.ini

 [pytest]
-addopts = --cov=nni --cov-config=.coveragerc --junitxml=junit/test-results.xml --cov-report=xml --cov-report=html --cov-config=.coveragerc
+addopts = --cov=nni --cov-config=.coveragerc --junitxml=junit/test-results.xml --cov-report=xml --cov-report=html --cov-config=.coveragerc --durations=50
 filterwarnings =
     ignore:Using key to access the identifier of:DeprecationWarning
     ignore:layer_choice.choices is deprecated.:DeprecationWarning