API Request: Finalize client side registration and report authentication

[rtamalin]

The /register REST API request obtains an auth token which needs to be included in the /report REST API request's headers as an Authorization header using the Bearer schema.

Additionally if a /report REST API request fails with a HTTP 401 Unauthorized this should:

• clear the existing auth token to indicate that a new auth token needs to be collected
• trigger an attempt to re-authenticate using the /authenticate REST API request.

Add support the /authenticate REST API request.

This work will be interdependent with that of the SUSE/telemetry-server#35 issue.

[rtamalin]

38 and SUSE/telemetry-server#39 complete this work.

Telemetry report submissions must include:

• an Authorization header in the Bearer schema specifying the auth token
• an X-Telemetry-Client-Id specifying the client's id

The server will reject the request with HTTP 401 Unauthorized if the supplied auth token is not valid, or the client is not registered with the server, or the auth token doesn't match what the server has recorded for the client.