Improve installation process

`meson.build` rewritten with DRY principle. `deploy.sh` added,
which deploys the image on a installation USB stick borrowed from
another project. Image name aligned with the installer's expectations.

vm.sh

@@ -9,7 +9,7 @@ fi
 qemu-system-x86_64 \
   "${debug_flags[@]}" \
   -monitor stdio \
-  -drive file=build/os.img,format=raw,if=none,id=nvme0 \
+  -drive file=build/os.raw,format=raw,if=none,id=nvme0 \
   -device nvme,drive=nvme0,serial=foo \
   -device qemu-xhci,id=xhci,msi=off,msix=off \
   -device usb-kbd,bus=xhci.0 \