When configuring serial, parallel, console or channel devices
with a file, dev or pipe backend type, it is necessary to label
the file path in the security drivers. For char devices of type
file, it is neccessary to pre-create (touch) the file if it does
not already exist since QEMU won't be allowed todo so itself.
dev/pipe configs already require the admin to pre-create before
starting the guest.

* src/qemu/qemu_security_dac.c: set file ownership for character
  devices
* src/security/security_selinux.c: Set file labeling for character
  devices
* src/qemu/qemu_driver.c: Add character devices to cgroup ACL