Support on demand instances

[mKeRix]

Recently I've hit the issue that AWS is out of capacity for the g3 instances in eu-central-1 quite often. To still be able to play I would like to have an option which allows me to spin up an on demand instance of the same type if no spot capacity is available.

I just skimmed through the code and am guessing that most of the process can be kept the same even for on demand instances - it seems like only a few spots in the code specifically do something with the spot APIs.

[NitriKx]

I was thinking of using the AutoScaling group feature that tries to fill in the requested capacity with spot instances, and fallback to ondemand in case there is not more spot.
It's also possible with the AutoScaling groups to define multiple instance templates, and let it decides which is the cheapest type (with spot or ondemand).

[dropitlikecross]

I'd also like to suggest ontop of the autoscaling, the ability to select only on demand as an extra option.

[NitriKx]

It seems that AutoScaling groups does not work in CloudRIG case as we need to stop the instance before creating an image from it: within an ASG the spot requests created are "one-time" and the underlying instances can not be stopped.
That's why I've implemented something based on SpotFleet instead.
We can imagine in the future to create a on-demand dedicated cloudformation template.