Description of problem:
Virtio-gpu should be supported as secondary gpu in libvirt

Version-Release number of selected component (if applicable):
libvirt: libvirt-2.0.0-5.el7.x86_64
qemu-kvm-rhev:qemu-kvm-rhev-2.6.0-21.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1.guest xml:
# cat virtiovga.xml 
<domain type="kvm">
  <name>rhel7.2</name>
  <uuid>70433aaf-752b-43e7-8c09-38d856bb24be</uuid>
  <memory>1048576</memory>
  <currentMemory>1048576</currentMemory>
  <vcpu>1</vcpu>
  <os>
    <type arch="x86_64">hvm</type>
  </os>
  <features>
    <acpi/>
    <apic/>
    <vmport state="off"/>
  </features>
  <cpu mode="custom" match="exact">
    <model>Haswell-noTSX</model>
  </cpu>
  <clock offset="utc">
    <timer name="rtc" tickpolicy="catchup"/>
    <timer name="pit" tickpolicy="delay"/>
    <timer name="hpet" present="no"/>
  </clock>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <pm>
    <suspend-to-mem enabled="no"/>
    <suspend-to-disk enabled="no"/>
  </pm>
  <devices>
    <emulator>/usr/libexec/qemu-kvm</emulator>
    <disk type="file" device="disk">
      <driver name="qemu" type="qcow2"/>
      <source file="/home/rhel73.qcow2"/>
      <target dev="vda" bus="virtio"/>
    </disk>
    <controller type="usb" index="0" model="ich9-ehci1"/>
    <controller type="usb" index="0" model="ich9-uhci1">
      <master startport="0"/>
    </controller>
    <controller type="usb" index="0" model="ich9-uhci2">
      <master startport="2"/>
    </controller>
    <controller type="usb" index="0" model="ich9-uhci3">
      <master startport="4"/>
    </controller>
    <interface type="bridge">
      <source bridge="br0"/>
      <mac address="52:54:00:ae:39:82"/>
      <model type="virtio"/>
    </interface>
    <input type="tablet" bus="usb"/>
	<graphics type='spice' port='-1' autoport='yes'>
    		<channel name='main' mode='insecure'/>
    		<channel name='record' mode='insecure'/>
    		<image compression='auto_glz'/>
    		<streaming mode='filter'/>
    		<clipboard copypaste='no'/>
    		<mouse mode='client'/>
    		<filetransfer enable='no'/>
  	</graphics>
    <console type="pty"/>
    <channel type="unix">
      <source mode="bind"/>
      <target type="virtio" name="org.qemu.guest_agent.0"/>
    </channel>
    <channel type="spicevmc">
      <target type="virtio" name="com.redhat.spice.0"/>
    </channel>
    <sound model="ich6"/>
    <video>
      <model type="virtio" primary="yes"/>
    </video>
    <video>
      <model type="virtio" primary="no"/>
    </video>
    <redirdev bus="usb" type="spicevmc"/>
    <redirdev bus="usb" type="spicevmc"/>
  </devices>
</domain>

2.
# virsh create virtiovga.xml 
error: Failed to create domain from virtiovga.xml
error: unsupported configuration: non-primary video device must be type of 'qxl'
3.

Actual results:
non-primary video device only support qxl

Expected results:
non-primary video device also support virtio-gpu

Additional info: