Add support for Spot fleets

[sylvinus]

See documentation about the feature here:
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/spot-fleet.html

Adding a --spot-fleet-request-config flag that points to the user-supplied config.json file would be great!

[nchammas]

@sylvinus - Can you summarize the value of this feature to you and contrast it with auto-scaling groups? I haven't used either feature, but it looks like you can launch spot instances as part of an auto-scaling group, so I'm wondering what the difference is.

[sylvinus]

@nchammas I think what Spot fleets add is the notion of instance weight, to be able to mix instance types in order to take advantage of lower spot prices and fall back automatically to other launch configurations when prices surge.

I have not used the feature myself yet but it's definitely something I'd test.