Account for runtime annotations that oveerwrite build time annotations

[cmainas]

Urunc makes use of annotations to get information about the sandbox type, guest kernel path, etc.. These annotations are constructed at build time through bunny. However, there are cases where these annotations can get overwritten by annotations a t runtime. For exmaple cloud-hypervisor and firecracker are using the same boot protocol (PVH) and therefore the same guest image can boot in both monitors. As a result, a urunc image built for firecracker can be also spawned over cloud-hypervisor if we simply specify the annotation com.urunc.unikernel.hypervisor at runtime.

[cmainas]

Tagging, so I can assign this @jiwahn.

[jiwahn]

Thanks, I’ll take a look at it!