Rule out testcase 660 from no-image variant

Test case 660 test for the behaviour of compiler when pre-initialize
classes into app image, for test with --no-image flag, the compiler will
not try to generate app image hence won't do pre-initialization, which
break the assumptions in the test case.

Test: testrunner.py --host --no-image -t 660
Change-Id: I87889c8af73065823443fa974b9e812f5b959e53
diff --git a/test/knownfailures.json b/test/knownfailures.json
index 53611a8..ffcd522 100644
--- a/test/knownfailures.json
+++ b/test/knownfailures.json
@@ -712,5 +712,10 @@
                          "lookup changes" ],
         "bug": "b/63089991",
         "env_vars": {"ANDROID_COMPILE_WITH_JACK": "false"}
+    },
+    {
+        "tests": "660-clinit",
+        "variant": "no-image",
+        "description": "Tests <clinit> for app images, which --no-image doesn't do"
     }
 ]