adding support for cloud-init and cloud-initramfs-growpart

installing cloud-init would allow machine to contact the metadata service exposed on 169.254.169.254, which can be useful to bootstrap a machine and run custom scripts like for monitoring , so that every stemcell which gets provisioned to a machine at the time of booting will get automatic monitored.
installing cloud-initramfs-growroot will allow stemcell to grow root partition according to the flavor.