xenserver: Make primary management interface on VLAN possible.

xenserver: Make primary management interface on VLAN possible.

Before xapi puts the primary management interface on a new PIF, it verifies
that the PIF's network device exists and has an IP address.  For physical
PIFs and for bonds, this works fine.  For VLANs, the openvswitch does not
put the IP address on the network device that xapi expects, but on a
different network device (e.g. openvswitch puts it on eth0.X instead of on
xapiY), so this checks fails with the message "The specified interface
cannot be used because it has no IP address".

This commit makes interface-reconfigure "fake out" xapi by putting a
dummy IP address on the xapi# interface.

Bug #1325.