Feature #2917: Rewrite onegate's urls to:
- /service
- /vm
Feature #2917: Inject ONEGATE_ENDPOINT to the context, instead of the URL and adds the VMID
Feature #2917: Authenticate using X_ONEGATE_VMID
Feature #2917: Add a generic GET / to ONEGATE and refactor code.
Feature #2917: Reformat onegate's reponses to match those of oneflow
Feature #2917: Overwrite ONEGATE_ENDPOINT in the context even if the user has defined it in the user template