CI: Initialization - Add Azure Pipelines for checking format and running pytest (#2)

**Description**
Init Azure Pipelines for checking format and running pytest.

**Major Revision**
- Add  azure-pipelines.yml for running Azure Pipelines.
- Add Dockerfile and test/test_example.py for checking format and running pytest. 

azure-pipelines.yml

+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT license.
+
+# Starter pipeline
+# Start with a minimal pipeline that you can customize to build and deploy your code.
+# Add steps that build, run tests, deploy, and more:
+# https://aka.ms/yaml
+
+trigger:
+- master
+- dev
+
+resources:
+- repo: self
+
+variables:
+  tag: '$(Build.BuildId)'
+
+steps:
+  - task: Docker@2
+    displayName: Build uni-test Docker for SuperBench testing
+    inputs:
+      command: build
+      dockerfile: '$(Build.SourcesDirectory)/test.dockerfile'
+      tags: |
+        $(tag)

test.dockerfile

+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT license.
+
+FROM ubuntu:18.04
+
+# Install the python3.7 and pip
+RUN apt-get update && apt-get install -y \
+    python3.7-dev \
+    python3-pip
+
+# Change default python3 version to python3.7
+RUN update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.6 1 && \
+    update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.7 10
+
+# Upgrade pip and instll flake8 and pytest 
+RUN python3 -m pip install --upgrade pip && \
+    python3 -m pip install flake8 pytest
+
+# Create workspace
+WORKDIR /superbench
+COPY . /superbench
+
+# Check code format using flake8 
+RUN python3 -m flake8
+    
+# Install library and run pytest
+RUN python3 -m pytest -v

tests/test_example.py

+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT license.
+
+# content of test_sample.py
+# get it from https://docs.pytest.org/en/stable/
+
+def inc(x):
+    return x + 1
+
+
+def test_answer():
+    assert inc(3) == 4