Change message into serverResponse and make it private - RES-928

[danielamihalache]

As a developer I need to change the message variable name and make it private in order to be not be confused with mail message. Dependencies: https://github.com/sendgrid/google-java-sample-app/pull/1

• [x] CR'd
• [x] QA'd
• [x] Dependencies satisfied
• [x] Ready to deploy