appveyor: do not pass integration jobs on failed unit tests

appveyor.yml

@@ -1,6 +1,8 @@
 environment:
   matrix:
     # Unit and integration tests.
+    - PYTHON: "C:\\Python27"
+    - PYTHON: "C:\\Python36-x64"
     - PYTHON: "C:\\Python27"
       RUN_INTEGRATION_TESTS: "True"
     - PYTHON: "C:\\Python36-x64"
@@ -58,8 +60,10 @@ test_script:
             subst T: $env:TEMP
             $env:TEMP = "T:\"
             $env:TMP = "T:\"
-            tox -e py -- -m unit -n 3
             if ($env:RUN_INTEGRATION_TESTS -eq "True") {
                 tox -e py -- -m integration -n 3 --duration=5
             }
+            else {
+                tox -e py -- -m unit -n 3
+            }
         }