gm self-test: use a pathologically simple test case instead of dashing2

gm/tests/outputs/compared-against-different-pixels-images/output-expected/json-summary.txt

 {
    "actual-results" : {
       "failed" : {
-         "565/dashing2" : {
-            "checksum" : FAKE
+         "565/selftest1" : {
+            "checksum" : 9948284449770991531
          },
-         "8888/dashing2" : {
-            "checksum" : FAKE
+         "8888/selftest1" : {
+            "checksum" : 9948284449770991531

[borenet, 2013/03/01 13:38:28]

I didn't realize that 8888 and 565 would end up with the same checksum when we
used pixel-based checksums.  I suspect that having inconsistent formats in the
GS image bucket will cause problems.  We should make sure to only upload one
format (8888?) for consistency.

          }
       },
       "failure-ignored" : null,
       "no-comparison" : null,
       "succeeded" : null
    },
    "expected-results" : {
-      "565/dashing2" : {
-         "checksums" : [ FAKE ],
+      "565/selftest1" : {
+         "checksums" : [ 8143889227369140487 ],
          "ignore-failure" : false
       },
-      "8888/dashing2" : {
-         "checksums" : [ FAKE ],
+      "8888/selftest1" : {
+         "checksums" : [ 8143889227369140487 ],
          "ignore-failure" : false
       }
    }
 }