move test execution into test stage

Author: sjaeckel

appveyor.yml

@@ -7,4 +7,6 @@ build_script:
   - if "Visual Studio 2015"=="%APPVEYOR_BUILD_WORKER_IMAGE%" call "C:\Program Files\Microsoft SDKs\Windows\v7.1\Bin\SetEnv.cmd" /x64
   - if "Visual Studio 2015"=="%APPVEYOR_BUILD_WORKER_IMAGE%" call "C:\Program Files (x86)\Microsoft Visual Studio 14.0\VC\vcvarsall.bat" x86_amd64
   - nmake -f makefile.msvc all
+
+test_script:
   - test.exe