OpenVZ: take veid from vmdef->name when defining new domains

OpenVZ: take veid from vmdef->name when defining new domains

We currently use the next free veid although there's one given in the
domain xml. This currently breaks defining new domains since vmdef->name
and veid don't match leading to the following error later on:

    error: Failed to define domain from 110.xml
    error: internal error Could not set UUID

Since silently ignoring vmdef->name is not nice respect it instead. We
avoid veid collisions in the upper levels already.