Comment 6 for bug 1471307

Tried other two cases:

1. boot from image without swap, then attach a volume to vdb, then resize to a flavor with swap, no swap disk created:

ubuntu@node-01:~$ virsh dumpxml 6 | grep -C 2 "target dev"
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/opt/stack/data/nova/instances/63c4ddd7-baf8-43a7-b282-3690a0c72d0a/disk'/>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
--
      <driver name='qemu' type='raw' cache='none'/>
      <source dev='/dev/disk/by-path/ip-10.239.47.37:3260-iscsi-iqn.2010-10.org.openstack:volume-35e63899-617b-405a-952f-f2a12b527d40-lun-1'/>
      <target dev='vdb' bus='virtio'/>
      <serial>35e63899-617b-405a-952f-f2a12b527d40</serial>
      <alias name='virtio-disk1'/>
--
      <mac address='fa:16:3e:56:e4:92'/>
      <source bridge='qbr42f2dab5-68'/>
      <target dev='tap42f2dab5-68'/>
      <model type='virtio'/>
      <alias name='net0'/>

2. boot from image without swap, then resize to a flavor with swap, swap disk was created and attached:
ubuntu@node-01:~$ virsh dumpxml 8 | grep -C 2 "target dev"
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/opt/stack/data/nova/instances/9bddc01e-b3a3-4cad-9861-132c4e4c6e1e/disk'/>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
--
      <driver name='qemu' type='qcow2' cache='none'/>
      <source file='/opt/stack/data/nova/instances/9bddc01e-b3a3-4cad-9861-132c4e4c6e1e/disk.swap'/>
      <target dev='vdb' bus='virtio'/>
      <alias name='virtio-disk1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
--
      <mac address='fa:16:3e:31:51:a5'/>
      <source bridge='qbr23992767-81'/>
      <target dev='tap23992767-81'/>
      <model type='virtio'/>
      <alias name='net0'/>