appveyor: make tests verbose

Reviewed-by: NMatt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1686)

appveyor.yml

@@ -39,7 +39,7 @@ build_script:
 
 test_script:
     - cd _build
-    - nmake test
+    - nmake test V=1
     - cd ..
 
 # Fake deploy script to test installation