Add install guide for Japanese language testing

Test the Japanese Install Guide as well.

Change-Id: I3ff73c2114bb7f31b0d50b17b46d7175dfb88e51

tools/test-languages.sh

@@ -37,7 +37,7 @@ function test_manuals {
 
 function test_ja {
     setup_lang 'ja' 'user-guide'
-    test_manuals 'ja' 'security-guide' 'high-availability-guide'
+    test_manuals 'ja' 'security-guide' 'high-availability-guide' 'install-guide'
 }