Auto-virtual-host capable munin-asyncd

If a munin-node has multiple virtual nodes, munin-asyncd fetches data only from a single node which is on the same host munin-node is running. Currently, there is no way to have munin-asyncd to access other virtual nodes. So, I enhanced munin-asyncd to fetch data from all virtual nodes. I believe this is what is called "auto-virtual-host capable" in Milestone Munin 2.2 (http://munin-monitoring.org/milestone/Munin%202.2).

Enhanced minin-asyncd will obtain virtual node names by the response of "nodes" command from nunin-node. If the response is as follows:

vnode1
vnode2
.

, minin-asyncd will fetch data from these virtual nodes and spool data at $SPOOLDIR/vnode1, $SPOOLDIR/vnode2.