[CI] Fix broken Docker container 'cpu' (#5956)

tests/ci_build/Dockerfile.cpu

@@ -19,13 +19,9 @@ ENV PATH=/opt/python/bin:$PATH
 
 ENV GOSU_VERSION 1.10
 
-# Install Python packages in default env
-RUN \
-    pip install pyyaml cpplint pylint astroid sphinx numpy scipy pandas matplotlib sh \
-    		recommonmark guzzle_sphinx_theme mock breathe graphviz hypothesis\
-		pytest scikit-learn wheel kubernetes urllib3 jsonschema boto3 && \
-    pip install https://h2o-release.s3.amazonaws.com/datatable/stable/datatable-0.7.0/datatable-0.7.0-cp37-cp37m-linux_x86_64.whl && \
-    pip install "dask[complete]"
+# Create new Conda environment
+COPY conda_env/cpu_test.yml /scripts/
+RUN conda env create -n cpu_test --file=/scripts/cpu_test.yml
 
 # Install lightweight sudo (not bound to TTY)
 RUN set -ex; \

tests/ci_build/conda_env/cpu_test.yml

@@ -0,0 +1,33 @@
+name: cpu_test
+channels:
+- conda-forge
+dependencies:
+- python=3.7
+- pip
+- wheel
+- pyyaml
+- cpplint
+- pylint
+- numpy
+- scipy
+- scikit-learn
+- pandas
+- matplotlib
+- dask
+- python-graphviz
+- hypothesis
+- astroid
+- sphinx
+- sh
+- recommonmark
+- mock
+- breathe
+- pytest
+- python-kubernetes
+- urllib3
+- jsonschema
+- boto3
+- awscli
+- pip:
+  - guzzle_sphinx_theme
+  - datatable

tests/ci_build/runxgb.sh

@@ -1,5 +1,7 @@
 #!/bin/bash
 
+source activate cpu_test
+
 export DMLC_SUBMIT_CLUSTER=local
 
 submit="python3 dmlc-core/tracker/dmlc-submit"

tests/ci_build/test_python.sh

@@ -45,6 +45,7 @@ case "$suite" in
     ;;
 
   cpu)
+    source activate cpu_test
     install_xgboost
     pytest -v -s --fulltrace tests/python
     cd tests/distributed