mantle: add support for IBM cloud

[dustymabe]

I'm breaking the mantle codebase work out of #277 since we can deliver an IBM cloud image without having image upload and kola (CI) test support. But we do want image upload and kola (CI) test support so we'll track it here. In order to achieve this goal we would want to update mantle within coreos-assembler to:

• Vendor golang library for platform (IBM's go SDK)
  • under https://github.com/coreos/coreos-assembler/tree/master/mantle/vendor
• Add low-level support code to platform/api
  • https://github.com/coreos/coreos-assembler/tree/master/mantle/platform/api
• Add any test code for low-level code to cmd/ore
  • https://github.com/coreos/coreos-assembler/tree/master/mantle/cmd/ore
• Add high-level API to platform/machine
  • platform/machine has a lot of boilerplate, so copying an existing platform is a good start
  • https://github.com/coreos/coreos-assembler/tree/master/mantle/platform/machine
• Plumb options from high-level API into cmd/kola/options.go
  • https://github.com/coreos/coreos-assembler/blob/master/mantle/cmd/kola/options.go

The two previous examples when we added a platform can also be useful for inspiration. The last two platforms that were added are Aliyun and Azure:

• Aliyun
  • *: add aliyun mantle#1066
• Azure
  • platform/azure: add kola/ore commands for Azure mantle#771