CLOUDSTACK-2652: requests module differs on Python 2.6

On 2.6 response.json returns the JSOn in the response while on 2.7
response.json() is a method. Since Marvin installs on both platforms
fixing the error appropriately

Signed-off-by: Prasanna Santhanam <tsp@apache.org>
CLOUDSTACK-1191: rbd: Use cloning for deploying templates instead of a copy

RBD format 2 supports cloning (aka layering) where one base image can serve
as a parent image for multiple child images.

This enables fast deployment of a large amount of virtual machines, but it also
saves spaces on the Ceph cluster and improves performance due to better caching.

Qemu-img doesn't support RBD format 2 (yet), so to enable these functions the
RADOS/RBD Java bindings are required.

This patch also enables deployment of System VMs on RBD storage pools. Since we
no longer require a patchdisk for passing the boot arguments we are able to deploy
these VMs on RBD.