Fix AppVeyor build - Python versions

appveyor.yml

@@ -8,31 +8,34 @@ environment:
  PAHO_BUILD_STATIC: FALSE
  PAHO_BUILD_SHARED: TRUE
  PAHO_HIGH_PERFORMANCE: FALSE
+ PYTHON_VERSION: Python36
  - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
  PAHO_WINDOWS_BUILD_BIT: x64
  OPENSSL_ROOT_DIR: "C:/OpenSSL-Win64"
  PAHO_BUILD_STATIC: TRUE
  PAHO_BUILD_SHARED: FALSE
  PAHO_HIGH_PERFORMANCE: TRUE
+ PYTHON_VERSION: Python36
  - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
  PAHO_WINDOWS_BUILD_BIT: x86
  OPENSSL_ROOT_DIR: "C:/OpenSSL-Win32"
  PAHO_BUILD_STATIC: FALSE
  PAHO_BUILD_SHARED: TRUE
  PAHO_HIGH_PERFORMANCE: TRUE
+ PYTHON_VERSION: Python37
 
 configuration: Debug
 install:
  - cmd: ver
  - cmd: openssl version
- - cmd: C:\Python36\python --version
- - cmd: netsh advfirewall firewall add rule name="Python 3.6" dir=in action=allow program="C:\Python36\python.exe" enable=yes
+ - cmd: C:\%PYTHON_VERSION%\python --version
+ - cmd: netsh advfirewall firewall add rule name="Python 3" dir=in action=allow program="C:\%PYTHON_VERSION%\python.exe" enable=yes
  - cmd: netsh advfirewall firewall add rule name="Open Port 1883" dir=in action=allow protocol=TCP localport=1883
  - cmd: netsh advfirewall set allprofiles state off
- - ps: Start-Process C:\Python36\python -ArgumentList 'test\mqttsas.py'
+ - ps: Start-Process C:\$Env:PYTHON_VERSION\python -ArgumentList 'test\mqttsas.py'
  - cmd: git clone https://github.com/eclipse/paho.mqtt.testing.git
  - cmd: cd paho.mqtt.testing\interoperability
- - ps: Start-Process C:\Python36\python -ArgumentList 'startbroker.py -c localhost_testing.conf'
+ - ps: Start-Process C:\$Env:PYTHON_VERSION\python -ArgumentList 'startbroker.py -c localhost_testing.conf'
  - cmd: cd ..\..
 
 build_script: