Update zfs-install

The guide includes working install of regular, hardened sources to be installed along with or without LUKS.

 This guide is highly influenced by 
1.https://mthode.org/posts/2013/Sep/gentoo-hardened-zfs-rootfs-with-dm-cryptluks-062/
2.https://github.com/codingenesis/zfs-overlay/blob/master/zfs-install

I have just added necessary changes to make the installation of ZFS more smooth and trouble free.