security: don't relabel chardev source if virtlogd is used as stdio handler

security: don't relabel chardev source if virtlogd is used as stdio handler

In the case that virtlogd is used as stdio handler we pass to QEMU
only FD to a PIPE connected to virtlogd instead of the file itself.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1430988

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>