vhost_user: cleanup mem_table when

Signed-off-by: Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>
vhost_user: implement stop()

Signed-off-by: Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>
Merge pull request #291 from virtualopensystems/vhost_user_stop

Vhost user stop
move token buffer handling from a tick()'ed method to :push()
remove tick() traces
simplify :push()