Fix test infrastructure for pytest > 4 and bump CI pytest version (#728)

Issues were caused by
https://docs.pytest.org/en/latest/historical-notes.html#marker-revamp

Author: leezu

conftest.py

@@ -150,7 +150,7 @@ def test_not_ok_with_random_data():
 
     """
 
-    seed = request.node.get_marker('seed')
+    seed = request.node.get_closest_marker('seed')
     env_seed_str = os.getenv('MXNET_TEST_SEED')
 
     if seed is not None:

env/cpu/py2.yml

@@ -9,9 +9,9 @@ dependencies:
   - sphinx=1.7.7
   - spacy
   - nltk
-  - pytest<4
-  - flaky<4
-  - pytest-cov=2.6.0
+  - pytest=4.5.0
+  - flaky=3.5.3
+  - pytest-cov=2.7.1
   - mock<3
   - pytest-xdist<2
   - pip:

env/cpu/py3-master.yml

@@ -9,9 +9,9 @@ dependencies:
   - sphinx=1.7.7
   - spacy
   - nltk
-  - pytest<4
-  - flaky<4
-  - pytest-cov=2.6.0
+  - pytest=4.5.0
+  - flaky=3.5.3
+  - pytest-cov=2.7.1
   - mock<3
   - pytest-xdist<2
   - pip:

env/cpu/py3.yml

@@ -9,9 +9,9 @@ dependencies:
   - sphinx=1.7.7
   - spacy
   - nltk
-  - pytest<4
-  - flaky<4
-  - pytest-cov=2.6.0
+  - pytest=4.5.0
+  - flaky=3.5.3
+  - pytest-cov=2.7.1
   - mock<3
   - pytest-xdist<1.28
   - recommonmark

env/gpu/py2.yml

@@ -9,9 +9,9 @@ dependencies:
   - sphinx=1.7.7
   - spacy
   - nltk
-  - pytest<4
-  - flaky<4
-  - pytest-cov=2.6.0
+  - pytest=4.5.0
+  - flaky=3.5.3
+  - pytest-cov=2.7.1
   - mock<3
   - pytest-xdist<2
   - pip:

env/gpu/py3-master.yml

@@ -9,9 +9,9 @@ dependencies:
   - sphinx=1.7.7
   - spacy
   - nltk
-  - pytest<4
-  - flaky<4
-  - pytest-cov=2.6.0
+  - pytest=4.5.0
+  - flaky=3.5.3
+  - pytest-cov=2.7.1
   - mock<3
   - pytest-xdist<2
   - recommonmark

env/gpu/py3.yml

@@ -9,9 +9,9 @@ dependencies:
   - sphinx=1.7.7
   - spacy
   - nltk
-  - pytest<4
-  - flaky<4
-  - pytest-cov=2.6.0
+  - pytest=4.5.0
+  - flaky=3.5.3
+  - pytest-cov=2.7.1
   - mock<3
   - pytest-xdist<2
   - recommonmark

setup.py

@@ -69,6 +69,7 @@ def find_version(*file_paths):
             'sphinx-gallery',
             'sphinx_rtd_theme',
             'nbsphinx',
+            'flaky',
         ],
     },
 )