feat: Implement configuration to display pyenv version name (#140)

This behavior can be enabled via setting `use_pyenv` to true.
The "pyenv" prefix before the version name can be configured using `pyenv_prefix`.

ci/setup-test-env.yml

@@ -10,27 +10,16 @@ steps:
       versionSpec: "1.10"
     displayName: "Install a fixed version of Go"
 
-  # Because the Pipelines agent updates are out of sync, we can't install 3.6.9
-  # with PythonTool on macOS
-
+  # We are using pyenv to install Python for integration tests
   # Install Python
-  - task: UsePythonVersion@0
-    inputs:
-      versionSpec: "3.6.9"
-    displayName: "Install a fixed version of Python"
-    condition: not(eq(variables['Agent.OS'], 'Darwin'))
-  # Install Python (macOS)
   - script: |
       echo "##vso[task.setvariable variable=PYTHON_VERSION;]3.6.9"
       echo "##vso[task.setvariable variable=PYENV_ROOT;]$HOME/.pyenv"
-    condition: eq(variables['Agent.OS'], 'Darwin')
   - script: |
       curl https://pyenv.run | bash
       echo "##vso[task.setvariable variable=PATH;]$PYENV_ROOT/bin:$PYENV_ROOT/shims:$PATH"
-    condition: eq(variables['Agent.OS'], 'Darwin')
   - script: |
       eval "$(pyenv init -)"
       pyenv install $PYTHON_VERSION
       pyenv global $PYTHON_VERSION
-    condition: eq(variables['Agent.OS'], 'Darwin')
     displayName: "Install a fixed version of Python"