Description of problem:
nr=0 is reserved for virtconsole ,shouldn't be used for vioserialport .but it can be added if I exec device_add virtserialport twice

Version-Release number of selected component (if applicable):
3.10.0-50.el7.x86_64
qemu-kvm-rhev-1.5.3-19.el7.x86_64
seabios-bin-1.7.2.2-4.el7.noarch
sgabios-bin-0.20110622svn-3.el7.noarch
seabios-1.7.2.2-4.el7.x86_64


How reproducible:
100%

Steps to Reproduce:
1.Start VM w/ virtio-serial-pci
/usr/libexec/qemu-kvm -M pc-i440fx-rhel7.0.0 -cpu SandyBridge -enable-kvm -m 2G -smp 2,cores=2 -name bcao_win-7-32-netkvm -uuid 884e673a-1b4a-4385-a522-b3cc35ef4e18 -rtc base=localtime,clock=host,driftfix=slew -drive file=win8-64.qcow2,if=none,media=disk,serial=aaabbbccc,werror=stop,rerror=stop,cache=none,format=qcow2,id=drive-disk0 -device ide-drive,bus=ide.0,unit=1,physical_block_size=4096,logical_block_size=512,drive=drive-disk0,id=disk0 -drive file=/root/en_windows_8_enterprise_x64_dvd_917522.iso,if=none,media=cdrom,id=aa -device ide-drive,id=aa1,drive=aa,bootindex=1 -drive file=/usr/share/virtio-win/virtio-win.iso,media=cdrom,if=none,id=bb -device ide-drive,id=bb1,drive=bb -netdev tap,vhost=on,id=netdev0 -device e1000,netdev=netdev0,id=nic1,mac=1a:46:0b:ca:bc:7b -vnc :1 -vga std -monitor stdio -usb -device usb-tablet,id=tablet0 -global PIIX4_PM.disable_s3=0 -global PIIX_PM.disable_s4=0 -monitor unix:/tmp/tt,server,nowait -device virtio-serial-pci,id=serial0 -chardev socket,path=/tmp/socket,server,nowait,id=chardev0 -device virtserialport,id=port0,name=com.redhat.rhevm.vdsm,chardev=chardev0

2.(qemu)info qtree

3.(qemu)chardev-add socket,path=/tmp/socket1,server,nowait,id=chardev1
4.(qemu)device_add  virtserialport,id=port1,name=com.redhat.test,chardev=chardev1,nr=0

5.(qemu)info qtree

6.Repeat step4 again

7.(qemu)info qtree

Actual results:
after step 2:
  dev: virtio-serial-pci, id "serial0"
        ioeventfd = on
        vectors = 2
        class = 0x780
        indirect_desc = on
        event_idx = on
        max_ports = 31
        addr = 04.0
        romfile = <null>
        rombar = 1
        multifunction = off
        command_serr_enable = on
        class Class 0780, addr 00:04.0, pci id 1af4:1003 (sub 1af4:0003)
        bar 0: i/o at 0xc060 [0xc07f]
        bar 1: mem at 0xfebf1000 [0xfebf1fff]
        bus: virtio-bus
          type virtio-pci-bus
          dev: virtio-serial-device, id ""
            max_ports = 31
            bus: serial0.0
              type virtio-serial-bus
              dev: virtserialport, id "port0"
                chardev = chardev0
                nr = 1
                name = "com.redhat.rhevm.vdsm"
                port 1, guest off, host off, throttle off

After step 3 , chardev can be added successfully
After step 4 ,
    It prompts "Port number 0 on virtio-serial devices reserved for virtconsole                  devices for backward compatibility.
                Device initialization failed.
                Device 'virtserialport' could not be initialized"

After step5 ,results same as step2

After step6 ,it prompts "Property 'virtserialport.chardev' can't take value 'chardev1', it's in use"

After step7 :it shows nr =4294967295
  bus: virtio-bus
          type virtio-pci-bus
          dev: virtio-serial-device, id ""
            max_ports = 31
            bus: serial0.0
              type virtio-serial-bus
              dev: virtserialport, id "ཫCw"
                chardev = <null>
                nr = 4294967295
                name = "com.redhat.test"
                port -1, guest off, host off, throttle off
              dev: virtserialport, id "port0"
                chardev = chardev0
                nr = 1
                name = "com.redhat.rhevm.vdsm"
                port 1, guest off, host off, throttle off






Expected results:
after step 6, results should same as after step4
After step7 ,results should same as after step2 & step5

Additional info:
Try to boot guest w/ virtserialport with nr=0 ,failed to start .