[SURE-8496] Elemental should support bandwidth efficient distribution of OS patches

[kkaempf]

1. Elemental should support differential downloads for the OS images to minimize the bandwidth required to patch the systems. Alternatively, Elemental should support package-based patching, while still providing the security benefits of image based upgrades (resiliency against failed upgrades, immutable file system).

2. The download mechanism should be resilient and gracefully handling temporary connectivity issues (e.g. support resuming of partial downloads)

3. Elemental should support bandwidth management controls for downloading OS images, including the ability to throttle and restrict the downloads to specific time of day windows.