seclabel: fix regression in libvirtd restart

seclabel: fix regression in libvirtd restart

Commit b434329 has a logic bug: seclabel overrides don't set
def->type, but the default value is 0 (aka static).  Restarting
libvirtd would thus reject the XML for any domain with an
override of <seclabel relabel='no'/> (which happens quite
easily if a disk image lives on NFS), with a message:

2012-01-04 22:29:40.949+0000: 6769: error : virSecurityLabelDefParseXMLHelper:2593 : XML error: security label is missing

Fix the logic to never read from an override's def->type, and
to allow a missing <label> subelement when relabel is no.  There's
a lot of stupid double-negatives in the code (!norelabel) because
of the way that we want the zero-initialized defaults to behave.

* src/conf/domain_conf.c (virSecurityLabelDefParseXMLHelper): Use
type field from correct location.