Test() method now tries the connection token aquired

[rgolangh]

When the client has a token acquired by former authentication we should
use it to test the connection. It is not enough just to keep holding the
token state when in fact it is no longer valid.

Description of the Change

The change actually performs a simple request to the ovirt-engine API, using an OPTIONS
https method with the Bearer token. If the token is no longer valid the request fails
and a reauthentication is made, to acquire a new token.

Benefits

Long running application, that needs to to communicate with engine API can survive
events of session expirations or timeouts and tokens being removed, without
creating new connections over and over again, by using the Test() method.
This should save us from constant login attempts, and load on the session management module
in the engine.

Possible Drawbacks

It may be that we want to design the client in a way that it only uses auth token and not to really
perform login with user/pass. In that case we would need to change some of the behaviours.

Verification Process

Use the procedure described in the issue to verify #193 (comment)

Fixes: #193

@imjoey PTAL

[imjoey]

@rgolangh It makes sense and look good to me. Thanks for this.