JCLOUDS-457: Add polling strategy

The polling strategy interface for job operations
and a simple implementation class have been added.
This implementation waits an initial time and then
polls at regular intervals.
> Do you think I should do this in the javadoc, or maybe in the readme/getting started guide?

I would say the Javadoc should simply say "this method can be long-running and can be interrupted" for those methods where that is appropriate.

The Getting Started Guide should describe the provider in general, and also explain that the operations are long-running and can be interrupted. It could say something like "see the Javadoc to find out which methods can be interrupted", and perhaps give an example of how that could be done.