conf: domain: Refactor virDomainDiskDefParseXML
conf: domain: Refactor virDomainDiskDefParseXML

Use the new virXMLProp helpers and XPath queries to get rid of the old
style of iteration through element children.

Note that in case of def->blockio.logical_block_size,
def->blockio.physical_block_size and def->rotation_rate the wraparound
behaviour of 'virStrToLong_ui' was _not_ forward ported to the new code
as it makes no sense with the attributes.

Signed-off-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>
Reviewed-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>

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