Add Support for AKIs and ARIs using Tags

[greese]

When a client submits a request to launch a virtual machine and they want to use an ARI or AKI during the launch, they can specify it as tags:

options.withMetaData("ramdiskImageId", id); options.withMetaData("kernelImageId", id);

And the AWS implementation will properly launch the VM.

Similarly, the kernelImageId and ramdiskImageId tags should be reflected in all VirtualMachine objects.

This approach should be backwards supported in 2013.01 even though a more cross-cloud implementation will be in effect.