ubuntu@localhost:~$ sudo snap install pi2-kernel_4.4.0-1017_armhf.snap 

error: cannot perform the following tasks:
- Mount snap "pi2-kernel" (unset) (cannot install kernel: cannot copy "/snap/pi2-kernel/x1/kernel.img" -> "/boot/uboot/pi2-kernel_x1.snap": exit status 1 ('/snap/pi2-kernel/x1/kernel.img' -> '/boot/uboot/pi2-kernel_x1.snap/kernel.img'
cp: failed to preserve ownership for '/boot/uboot/pi2-kernel_x1.snap/kernel.img': Operation not permitted