Use uncompressed kernel file to save memory

[hlinnaka]

If you pass an uncompressed kernel file to qemu, it will mmap() it directly into the address space. That can save some memory if the kernel image is used by many qemu processes, because the kernel can share the memory pages for each process.

See https://stefano-garzarella.github.io/posts/2019-12-22-qemu-kernel-initrd-mmapped/

Would be nice to test if that has a measurable effect in our fleet.

[cicdteam]

Just note. NeonVMs do not share a kernel. Each VM has its own kernel (yes, the same, but placed in different paths in the docker overlay filesystem).