Fix unit test

[ethantkoenig]

tempfile.mktemp does not actually create a file, so we would hit an error for trying to copy to a non-existent file.

e.g. (from https://travis-ci.org/unfoldingWord-dev/tx-manager/builds/343357743)

  File "/home/travis/build/unfoldingWord-dev/tx-manager/libraries/converters/converter.py", line 91, in run
    self.upload_archive()
  File "/home/travis/build/unfoldingWord-dev/tx-manager/libraries/converters/converter.py", line 131, in upload_archive
    App.cdn_s3_handler().upload_file(self.output_zip_file, self.cdn_file, cache_time=0)
  File "/home/travis/virtualenv/python2.7.13/lib/python2.7/site-packages/moto/core/models.py", line 70, in wrapper
    result = func(*args, **kwargs)
  File "/home/travis/build/unfoldingWord-dev/tx-manager/tests/client_tests/test_client_webhook.py", line 284, in mock_cdn_upload_file
    return self.upload_file(bucket_name, project_file, s3_key)
  File "/home/travis/virtualenv/python2.7.13/lib/python2.7/site-packages/moto/core/models.py", line 70, in wrapper
    result = func(*args, **kwargs)
  File "/home/travis/build/unfoldingWord-dev/tx-manager/tests/client_tests/test_client_webhook.py", line 292, in upload_file
    shutil.copyfile(project_file, filename)
  File "/opt/python/2.7.13/lib/python2.7/shutil.py", line 83, in copyfile
    with open(dst, 'wb') as fdst:
IOError: [Errno 2] No such file or directory: u'/tmp/test-tx-manager/tmp5QoEYZ'

[coveralls]

Coverage remained the same at 93.094% when pulling 8cf24aa on ethantkoenig:fix/tests into d3e0a44 on unfoldingWord-dev:develop.