doc: update vhost sample guide

doc: update vhost sample guide

For vhost-switch sample, the old guide takes too many words on
vhost-cuse, which is mainly due to vhost-cuse is invented before
vhost-user.

Now vhost-cuse is removed, meaning the best part of the doc is useless.
Instead of amending one piece here and there, this patch simply removes
the most part of the doc and replace it with a simple test guide.

For tep_term sample, mainly for removing the part has "vhost-cuse".

Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Acked-by: John McNamara <john.mcnamara@intel.com>