doc: add vhost-user to sample guide
doc: add vhost-user to sample guide

add vhost user documentation
fix some minor issues

Signed-off-by: Huawei Xie <3b3be4428106761300a2ee559c9f71ecdb091553@intel.com>

mixja/dpdk,msune/dpdk,msune/dpdk,venkynv/dpdk-mirror,msune/dpdk,venkynv/dpdk-mirror,mixja/dpdk,john-mcnamara-intel/dpdk,venkynv/dpdk-mirror,tsphillips/dpdk-fork,tsphillips/dpdk-fork,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,venkynv/dpdk-mirror,mixja/dpdk,tsphillips/dpdk-fork,tsphillips/dpdk-fork,mixja/dpdk,msune/dpdk,john-mcnamara-intel/dpdk