Add RHEL style kmod packages

Add RHEL style kmod packages

Provide a Redhat specific zfs-kmod.spec file which uses the old style
kmods (not kmods2) packaging.  By using the provided kmodtool script
packages can be built which support weak modules.  This allows for the
kernel to be updated without having to rebuild the ZFS kernel modules.

Packages for RHEL/Centos/SL/TOSS which use this spec file can by built
as follows:

$ ./configure --with-spec=redhat
$ make rpms

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>