Remove ovirt-pxe and ovirt-flash* wrapper scripts and provide docs in README

Remove ovirt-pxe and ovirt-flash* wrapper scripts and provide docs in README

ovirt-pxe and ovirt-flash scripts just wrapped livecd-iso-to-* functionality
and really did not provide any added value.  Only thing that ovirt-pxe did
that was valuable was added IPAPPEND 2 to the sample config file produced
by livecd-iso-to-pxe, but since in most configurations (cobbler etc) you
can't just use this file as is, instead we'll provide samples in README
and instructions for calling livecd-iso-to-* scripts directly.

Also, ovirt-node-image-pxe subpackage provided no real value since
all it did was provide %post that ran ovirt-pxe.  So removed it.

Signed-off-by: Perry Myers <pmyers@redhat.com>