conf: Restore ctxt's node in right scope
conf: Restore ctxt's node in right scope

We just found <qemu:commandline> is ignored in our xml. Further debug
shows that ctxt's node pointer isn't restored in virDomainSecDefParseXML(),
which leads to parsing of remaining elements failed.

Signed-off-by: Zhenzhong Duan <0a6aad489bf65c23415e55e6bee033aa588b7328@intel.com>
Reviewed-by: Pavel Hrdina <d4772d05997b8abf035041e3b4f4996380ea7e7a@redhat.com>

nertpinx/libvirt,olafhering/libvirt,crobinso/libvirt,nertpinx/libvirt,crobinso/libvirt,zippy2/libvirt,zippy2/libvirt,nertpinx/libvirt,olafhering/libvirt,libvirt/libvirt,crobinso/libvirt,jfehlig/libvirt,libvirt/libvirt,jfehlig/libvirt,nertpinx/libvirt,zippy2/libvirt,nertpinx/libvirt,olafhering/libvirt,jfehlig/libvirt,libvirt/libvirt,crobinso/libvirt,olafhering/libvirt,zippy2/libvirt,libvirt/libvirt,jfehlig/libvirt