Fix security driver handling of FIFOs with QEMU

Fix security driver handling of FIFOs with QEMU

When setting up a FIFO for QEMU, it allows either a pair
of fifos used unidirectionally, or a single fifo used
bidirectionally. Look for the bidirectional fifo first
when labelling since that is more useful

* src/security/security_dac.c,
  src/security/security_selinux.c: Fix fifo handling