Google Cloud Storage target for luigi.

Mostly copy and paste of the S3Target with AWS api calls replaced with GCS calls. It has only two major differences:

• AFAIK we can't make resumable downloads in GCS
• for uploads file extention is required to make it possible to guess file mime type Without extension file will be treated as binary file

target = GcsTarget(path)

will create target with GCS account details loaded from default config file (/etc/gaw/gapi.yaml)

fs = GcsFileSystem(conf=dict_conf)
target = GcsTarget(path, gcs_filesystem=conf)

will create target with gcs conf provided by dictionary dict_conf

fs = GcsFileSystem(
  secret_key=gcs_secret_key_file_path, 
  email=gcs_email, 
  private_key_password=optional_password)
target = GcsTarget(path, gcs_filesystem=conf)

will create target that uses GCS account gcs_email identified by secret key stored in a file located at gcs_secret_key_file_path with password optional_password (which is "notasecret" by default)

Here is sample YAML file with all required and optional configuration options

gapi:
  auth:
    cert: './conf/privatekey.pem'
    password: 'notasecret'
    email: 'app-id@developer.gserviceaccount.com'