xenserver: Cleanup xs-network-uuids and xs-network-names usage

xenserver: Cleanup xs-network-uuids and xs-network-names usage

Switch xs-network-uuids delimiter to a semicolon to match the one used
by xs-network-uuids.  Also, fix pluralization of xs-network-uuids in
vswitch IDL description of the "Bridge" table.

Add description of xs-network-names to vswitch IDL description.