Incorrectly sets BlockDeviceMapping.1.Ebs.DeleteOnTermination for non-EBS mapped volumes

[ianatha]

As of 9e419ba, a request like Action=RunInstances&BlockDeviceMapping.1.DeviceName=%2Fdev%2Fsdb&BlockDeviceMapping.1.Ebs.DeleteOnTermination=false&BlockDeviceMapping.1.VirtualName=ephemeral0 will be generated for the following BlockDeviceMapping array:

block_devices := []ec2.BlockDeviceMapping{
    ec2.BlockDeviceMapping{
        DeviceName: "/dev/sdb",
        VirtualName: "ephemeral0",
    },
}

(There should be no BlockDeviceMapping.1.Ebs.DeleteOnTermination.)

However, this causes EC2 to interpret the BlockDeviceMapping as referring to an EBS volume (even though it could be referring to an instance-store volume).