Install give kernel to system.
Called by make install on Linux 4.0.
On Ubuntu 14.04, furnished by the debianutils package.
It does a:
/run-parts /etc/kernel/postinst.d
which runs all scripts under /etc/kernel/postinst.d. Files in that directory are furnished by several packages.
In particular, this also runs update-grub via /etc/kernel/postinst.d/zz-update-grub.