ostree: move boot files out from /boot
Ostree have a special handling for populating boot files
(kernel/initramfs/dtb) from deployed commit.
It may use /boot or /usr/lib/ostree-boot source directories
from deployment to generate bootable configuration for given bootloader.
Move all files from deployment /boot to /usr/lib/ostree-boot to
avoid systemd confusion during boot -- /boot directory must be empty.
Changed setup-boot function to pass additional agrument with a target
directory where to put all bootables.
Edited by Denis Pynkin