Add init scripts

Add init scripts

To support automatically mounting your zfs on filesystem on boot
a basic init script is needed.  Unfortunately, every distribution
has their own idea of the _right_ way to do things.  Rather than
write one very complicated portable init script, which would be
invariably replaced by the distributions own anyway.  I have
instead added support to provide multiple distribution specific
init scripts.

The correct init script for your distribution will be selected
by ZFS_AC_DEFAULT_PACKAGE which will set DEFAULT_INIT_SCRIPT.
During 'make install' the correct script for your system will
be installed from zfs/etc/init.d/zfs.DEFAULT_INIT_SCRIPT to the
usual /etc/init.d/zfs location.

Currently, there is zfs.fedora and a more generic zfs.lsb init
script.  Hopefully, the distribution maintainers who know best
how they want their init scripts to function will feedback their
approved versions to be included in the project.

This change does not consider upstart jobs but I'm not at all
opposed to add that sort of thing.