Description of problem:
Set security_default_confined = 0 and security_require_confined = 1 in qemu.conf, and set dynamic selinux in domain xml, guest failed to start:
# virsh dumpxml rhel7
...
  <seclabel type='dynamic' model='selinux' relabel='yes'/>
...

# virsh start rhel7
error: Failed to start domain rhel7
error: unsupported configuration: Unconfined guests are not allowed on this host

Version-Release number of selected component:
libvirt-2.0.0-5.el7.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Config qemu.conf as below and restart libvirtd service:
# grep '^security' /etc/libvirt/qemu.conf
security_default_confined = 0
security_require_confined = 1

2. Start guest

Actual results:
Guest failed to start

Expected results:
Guest start successfully, because dac driver is enabled by default.

Additional info:
If set both selinux and dac security label in domain xml , guest will start successfully:
# virsh dumpxml rhel7
...
  <seclabel type='dynamic' model='selinux' relabel='yes'/>
  <seclabel type='dynamic' model='dac' relabel='yes'/>
...

# virsh start rhel7
Domain rhel7 started