Initial draft for spot instance requests from the Amazon tutorial
Working process test for creating Amazon spot instances

Moved the logic for spot requests in separate activities:
- cancel all requests
- predicates to check if requests are open or active
- option for the create command that enables you to specify the spot bid
- process variables, Activiti flow and context for the new activities
Fixed review issues

- added generic option for provider-specific properties with tests
- fixed formatting and comments
- better collection handling with Guava
- used polling & stopwatches instead of just sleeping when waiting for spot requests