Implement registration retry with exponential backoff

[ansasaki]

Currently, the agent does not retry registering with the registrar in case of failure. This is about implementing the registration retry with exponential backoff.

The idea is that the agent should keep trying to register itself with the registrar with exponential increasing wait time between retries. Probably it makes sense to limit the maximum wait time.

[sergio-correia]

I will work on this.