Refine OSB metadata provided in coab-vars.yml & git commit message

[gberche-orange]

As of OSB spec 2.14 described in CF profile, the org/space/service instance names are available in the context:

  "context": {
    "platform": "cloudfoundry",
    "organization_guid": "87505508-4c09-499e-933c-eb89582cb9a5",
    "space_guid": "30d49f4b-82bd-4e59-b90f-25a13a8a43dd",
    "organization_name": "system_domain",
    "space_name": "overview-broker",
    "instance_name": "my-service"
  },

Additionally, headers include x-api-info-location which is documented at https://docs.cloudfoundry.org/services/supporting-multiple-cf-instances.html and is making its way into the OSB specs into openservicebrokerapi/servicebroker#676

  "headers": {
[...]
    "[x-api-info-location": "donotuseapi.run.pivotal.io/v2/info",
[...]

Making these metadata available to git commit message makes it more friendly for operators.

Making these metadata available to coab-vars.yml enables templates authors to leverage it in their automation, e.g. to configure mysql dashboard with the right uaa, see cloudfoundry/cf-mysql-release#228

ps: pending PWS support question on donotuse prefix