Description of problem:
xml of scsi_generic and vports device fail to validate

Version-Release number of selected component (if applicable):
libvirt-4.4.0-2.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1. xml of scsi_generic device fail to validate:

# virsh nodedev-list --cap scsi_generic
scsi_generic_sg0

# virsh nodedev-dumpxml scsi_generic_sg0 > generic

# virt-xml-validate generic
generic:6: element capability: Relax-NG validity error : Element capability failed to validate content

# virsh nodedev-dumpxml scsi_generic_sg0 
<device>
  <name>scsi_generic_sg0</name>
  <path>/sys/devices/pci0000:00/0000:00:03.0/0000:09:00.0/host0/target0:2:0/0:2:0:0/scsi_generic/sg0</path>
  <devnode type='dev'>/dev/sg0</devnode>
  <parent>scsi_0_2_0_0</parent>
  <capability type='scsi_generic'>
    <char>/dev/sg0</char>
  </capability>
</device>

2. xml of HBA device failed to validate
# virsh nodedev-list --cap vports
scsi_host8
scsi_host9

# virsh nodedev-dumpxml scsi_host9 > host9
# virt-xml-validate host9
host9:7: element unique_id: Relax-NG validity error : Element capability has extra content: unique_id
host9 fails to validate

# virsh nodedev-dumpxml scsi_host9
<device>
  <name>scsi_host9</name>
  <path>/sys/devices/pci0000:00/0000:00:09.0/0000:18:00.0/host9</path>
  <parent>pci_0000_18_00_0</parent>
  <capability type='scsi_host'>
    <host>9</host>
    <unique_id>9</unique_id>
    <capability type='fc_host'>
      <wwnn>20000024ff370144</wwnn>
      <wwpn>21000024ff370144</wwpn>
      <fabric_wwn>ffffffffffffffff</fabric_wwn>
    </capability>
    <capability type='vport_ops'>
      <max_vports>254</max_vports>
      <vports>0</vports>
    </capability>
  </capability>
</device>

Actual results:
xml of scsi_generic and scsi_host(with vports) device fail to validate

Expected results:
should succeed to validate

Additional info:
fc_host without vport pass the validation
# virsh nodedev-list --cap fc_host
scsi_host10
scsi_host12
scsi_host8
scsi_host9

# virsh nodedev-list --cap vports
scsi_host8
scsi_host9

# virsh nodedev-dumpxml scsi_host12 > scsi_host
# virt-xml-validate scsi_host
scsi_host validates

# virsh nodedev-dumpxml scsi_host12
<device>
  <name>scsi_host12</name>
  <path>/sys/devices/pci0000:00/0000:00:09.0/0000:18:00.1/host8/vport-8:0-3/host12</path>
  <parent>scsi_host8</parent>
  <capability type='scsi_host'>
    <host>12</host>
    <unique_id>12</unique_id>
    <capability type='fc_host'>
      <wwnn>20000024ff370144</wwnn>
      <wwpn>2101001b32a90000</wwpn>
      <fabric_wwn>2001000dec9877c1</fabric_wwn>
    </capability>
  </capability>
</device>