Don't ignore build/test failures in Appveyor

Author: robinlinden

appveyor.yml

@@ -16,5 +16,4 @@ test_script:
   - set CONAN_CPU_COUNT=50
   - set CTEST_OUTPUT_ON_FAILURE=1
   - conan install -if _build -o with_tests=True .
-  - conan build -bf _build -if _build . &
-    exit 0
+  - conan build -bf _build -if _build .