When build log is not found, skip it and avoid 404.
Fixes exception
```
Traceback (most recent call last):
File "oss-fuzz/infra/gcb/builds_status.py", line 243, in <module>
main()
File "oss-fuzz/infra/gcb/builds_status.py", line 228, in main
status_filename='status.json')
File "oss-fuzz/infra/gcb/builds_status.py", line 159, in update_build_status
last_build = find_last_build(builds, project, build_tag_suffix)
File "oss-fuzz/infra/gcb/builds_status.py", line 102, in find_last_build
log.download_to_filename(f.name)
File "/var/jenkins_home/workspace/infra/builds_status/ENV/local/lib/python2.7/site-packages/google/cloud/storage/blob.py", line 565, in download_to_filename
file_obj, client=client, start=start, end=end)
File "/var/jenkins_home/workspace/infra/builds_status/ENV/local/lib/python2.7/site-packages/google/cloud/storage/blob.py", line 537, in download_to_file
_raise_from_invalid_response(exc)
File "/var/jenkins_home/workspace/infra/builds_status/ENV/local/lib/python2.7/site-packages/google/cloud/storage/blob.py", line 1873, in _raise_from_invalid_response
raise exceptions.from_http_response(error.response)
google.api_core.exceptions.NotFound: 404 GET https://www.googleapis.com/download/storage/v1/b/oss-fuzz-gcb-logs/o/log-9fca5dab-72bf-4970-9557-86b93ede51e0.txt?alt=media: No such object: oss-fuzz-gcb-logs/log-9fca5dab-72bf-4970-9557-86b93ede51e0.txt
Build step 'Execute shell' marked build as failure
Finished: FAILURE
```
* [infra] Publish build badges on status page
* Address feedback from github PR
* Change success badge to 'fuzzing' and failing badge to 'build failing'
Get a batch of the last 2000 builds, and filter on those ourselves
instead of calling the cloudbuild API to filter for us. The cloudbuild
API filtering API does not work with our number of builds.
Fixes#2263
* [infra] Use 'coverage' and 'fuzzing' tags to filter builds (follow-up #1547).
* Remove unintentional print call.
* Remove a variable that is not used anympre.