[tools] Post-filter clusterfuzz test cases with bugs

NOTRY=true
TBR=titzer@chromium.org

Bug: chromium:775027
Change-Id: I0bd4a55e3530e1e2f26bbe416587f1421f6cdbae
Reviewed-on: https://chromium-review.googlesource.com/721180Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48597}

tools/release/check_clusterfuzz.py

@@ -214,7 +214,8 @@ def Main():
     issues = APIRequest(key, **args)
     assert issues is not None
     for issue in issues:
-      if re.match(spec["crash_state"], issue["crash_state"]):
+      if (re.match(spec["crash_state"], issue["crash_state"]) and
+          not issue.get('has_bug_flag')):
         results.append(issue["id"])
 
   if options.results_file: