Expose the build variables via the REST API

At the moment, the metadata REST API expansion does not show the build variables. The following URL only provides the metadata: URL/rest/api/latest/result/TESTA-TSTA-JOB1-5?expand=metadata I will propose to have another expansion point "variables" so that we can use the URL URL/rest/api/latest/result/TESTA-TSTA-JOB1-5?expand=variables to expose the build variables.

This is originally raised from https://answers.atlassian.com/questions/191160/how-do-i-read-bamboo-custom-variables-via-the-rest-api