Bug 1625511

Description of problem:
Starting VM with several USB device failed after enabling USB suport because identifying USB device plugged to hub failed

Version-Release number of selected component (if applicable):
server: 
rhvm-4.2.5.1-0.1.el7ev.noarch

host: 
vdsm-4.20.39-1.el7ev.x86_64
kernel-3.10.0-942.el7.x86_64
libvirt-4.5.0-8.el7.x86_64
qemu-kvm-rhev-2.12.0-12.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1. New VM with several USB host device, disable USB support. start Vm successfully.
==> In this scenario, In XML, using 'piix3-uhci' USB controller which only supports 2 ports, so hub will be added, and several USB devices will be plugged to hub.
the dumpxml of VM is as following:
# virsh dumpxml jiyan-1
...
    <controller type='usb' index='0' model='piix3-uhci'>
      <alias name='usb'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
    </controller>
...
    <controller type='ccid' index='0'>
      <alias name='ccid0'/>
      <address type='usb' bus='0' port='1'/>
    </controller>
...
    <hub type='usb'>
      <alias name='hub0'/>
      <address type='usb' bus='0' port='2'/>
    </hub>
...
    <hostdev mode='subsystem' type='usb' managed='no'>
      <source>
        <address bus='2' device='2'/>
      </source>
      <alias name='ua-3ad599b3-069d-4849-8391-43cf97b17240'/>
      <address type='usb' bus='0' port='2.1'/>
    </hostdev>
    <hostdev mode='subsystem' type='usb' managed='no'>
      <source>
        <address bus='3' device='2'/>
      </source>
      <alias name='ua-6f48fe4c-fbb5-48c5-9ca5-852006b83510'/>
      <address type='usb' bus='0' port='2.2'/>
    </hostdev>
    <hostdev mode='subsystem' type='usb' managed='no'>
      <source>
        <address bus='2' device='3'/>
      </source>
      <alias name='ua-801d94ed-661b-45f2-a324-9f968d1363c0'/>
      <address type='usb' bus='0' port='2.3'/>
    </hostdev>
    <hostdev mode='subsystem' type='usb' managed='no'>
      <source>
        <address bus='3' device='4'/>
      </source>
      <alias name='ua-811d84bf-1a97-4fd8-b10d-ce14a98e52a6'/>
      <address type='usb' bus='0' port='2.4'/>
    </hostdev>
    <hostdev mode='subsystem' type='usb' managed='no'>
      <source>
        <address bus='3' device='3'/>
      </source>
      <alias name='ua-a16494ac-2a31-4639-95db-11f6dc8186f7'/>
      <address type='usb' bus='0' port='2.5'/>
    </hostdev>

2. Shut down VM, then ensble 'USB support', VM will start failed with the following error
2018-09-05 01:46:37,028-04 ERROR [org.ovirt.engine.core.dal.dbbroker.auditloghandling.AuditLogDirector] (ForkJoinPool-1-worker-11) [] EVENT_ID: VM_DOWN_ERROR(119), VM jiyan-1 is down with error. Exit message: XML error: there is no hub at port 2 in USB address bus: 0 port: 2.1.
2018-09-05 01:46:37,045-04 ERROR [org.ovirt.engine.core.vdsbroker.monitoring.VmsMonitoring] (ForkJoinPool-1-worker-11) [] Rerun VM '488061ac-89e5-4139-b01c-bcc6bd9e4119'. Called from VDS 'host5'
2018-09-05 01:46:37,061-04 WARN  [org.ovirt.engine.core.dal.dbbroker.auditloghandling.AuditLogDirector] (EE-ManagedThreadFactory-engine-Thread-233944) [] EVENT_ID: USER_INITIATED_RUN_VM_FAILED(151), Failed to run VM jiyan-1 on Host host5.

Actual results:
As step-2 shows

Expected results:
The XML should be adjusted automatically and VM should start successfully.

Additional info:
In step-2, the XML is as following, Checking this XML in ovirt-engine.log:

  43483     <controller type="usb" model="ich9-uhci1" index="0"/>
  43527     <controller type="usb" model="ich9-ehci1" index="0"/>
  43568     <controller type="usb" model="ich9-uhci2" index="0"/>
  43569     <controller type="usb" model="ich9-uhci3" index="0"/>
  ...
  43484     <hostdev managed="no" mode="subsystem" type="usb">
  43485       <source>
  43486         <address bus="2" device="2"/>
  43487       </source>
  43488       <alias name="ua-3ad599b3-069d-4849-8391-43cf97b17240"/>
  43489       <address bus="0" port="2.1" type="usb"/>
  43490     </hostdev>