Bug 1355659

Description of problem:
This is in rhel7.2 Z. Boot a guest with vhostuser server mode, QEMU will prompt code level warning messages after shutdown guest. 

Version-Release number of selected component (if applicable):
qemu-kvm-rhev-2.3.0-31.el7_2.18.x86_64

How reproducible:
10%

Steps to Reproduce:
1. Run a slirp/vlan in a background process
# /usr/libexec/qemu-kvm \
-net none \
-net socket,vlan=0,udp=localhost:4444,localaddr=localhost:5555 \
-net user,vlan=0

2. Start qemu with vhost-user as server mode
# /usr/libexec/qemu-kvm  -m 1024 -smp 2 \
-object memory-backend-file,id=mem,size=1024M,mem-path=/dev/hugepages,share=on \
-numa node,memdev=mem -mem-prealloc \
-chardev socket,id=char0,path=/tmp/vubr.sock,server \
-netdev type=vhost-user,id=mynet1,chardev=char0,vhostforce \
-device virtio-net-pci,netdev=mynet1,mac=54:52:00:1a:2c:01 \
/home/pezhang/rhel7.3.qcow2 \
-monitor stdio \
-vga std -vnc :10 \

3. Start vubr as vhostuser client
# ./vhost-user-bridge -c

4. Shutdown guest, qemu will print below messages.
(qemu) system_powerdown 
or
in guest:
# shutdown -h now 

(qemu) 
(process:16842): GLib-CRITICAL **: g_io_channel_write_chars: assertion 'channel != NULL' failed

(process:16842): GLib-CRITICAL **: g_io_channel_write_chars: assertion 'channel != NULL' failed

Actual results:
Qemu quit with printing code level warning messages. Seems it doesn't quit well.
(process:14946): GLib-CRITICAL **: g_io_channel_write_chars: assertion 'channel->is_writeable' failed

Expected results:
Qemu should quit without warning or error info.

Additional info:
1. gdb info
(qemu) 
(process:14946): GLib-CRITICAL **: g_io_channel_write_chars: assertion 'channel->is_writeable' failed

(process:14946): GLib-CRITICAL **: g_io_channel_write_chars: assertion 'channel->is_writeable' failed
(gdb) bt
No stack.

2. Previous version qemu-kvm-rhev-2.3.0-31.el7_2.17.x86_64 doesn't hit this issue.

3. This bug is found during verifying Bug 1351892 - vhost-user: A socket file is not deleted after VM's port is detached.