scripts/generate_index_pattern.py doesn't seem to be adding the default _feilds

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For confirmed bugs, please report:

• Version: master
• Operating System: OSX
• Steps to Reproduce:
  make update

It is not making these fields that if you don't push the beat-generated index-pattern and just let kibana figure it out it DOES create them:

 {\"name\":\"_id\",\"type\":\"string\",\"count\":0,\"scripted\":false,\"indexed\":false,\"analyzed\":false,\"doc_values\":false,\"searchable\":false,\"aggregatable\":false},

 {\"name\":\"_type\",\"type\":\"string\",\"count\":0,\"scripted\":false,\"indexed\":false,\"analyzed\":false,\"doc_values\":false,\"searchable\":true,\"aggregatable\":true},

 {\"name\":\"_index\",\"type\":\"string\",\"count\":0,\"scripted\":false,\"indexed\":false,\"analyzed\":false,\"doc_values\":false,\"searchable\":false,\"aggregatable\":false}

 {\"name\":\"_score\",\"type\":\"number\",\"count\":0,\"scripted\":false,\"indexed\":false,\"analyzed\":false,\"doc_values\":false,\"searchable\":false,\"aggregatable\":false}