Don't run test 2047 without an image

It relies on having a boot image for the CHECKer tests.

Test: Presubmit
Change-Id: I80e2fc07d6ff049a66714eea90482bd14d5322ee
diff --git a/test/knownfailures.json b/test/knownfailures.json
index 5a90e51..550b863 100644
--- a/test/knownfailures.json
+++ b/test/knownfailures.json
@@ -183,9 +183,10 @@
                   "138-duplicate-classes-check",
                   "018-stack-overflow",
                   "961-default-iface-resolution-gen",
-                  "964-default-iface-init-gen"],
+                  "964-default-iface-init-gen",
+                  "2047-checker-const-string-length"],
         "variant": "no-image",
-        "description": ["This test fails without an image. 018, 961, 964 often",
+        "description": ["137, 138, 2047 fail without an image. 018, 961, 964 often ",
                         "time out."],
         "bug": "http://b/34369284"
     },