Tried to reproduce on rhel 6, it fails nicely as it should:
$ /usr/libexec/qemu-kvm -incoming tcp:0:1234 -spice port=1234 /dev/zero ; echo "qemu-kvm return code: $?"
do_spice_init: starting 0.8.3
spice_server_add_interface: SPICE_INTERFACE_MIGRATION
spice_server_add_interface: SPICE_INTERFACE_KEYBOARD
spice_server_add_interface: SPICE_INTERFACE_MOUSE
spice_server_add_interface: SPICE_INTERFACE_QXL
red_worker_main: begin
Migration failed. Exit code tcp:0:1234(-98), exiting.
qemu-kvm return code: 158
Note for Virt QE: the reproducer on 5.x can be simplified to this universal command line so you don't have to re-create reporter's setup:
/usr/libexec/qemu-kvm -nographic -incoming tcp:0:1234 -spice port=1234 /dev/zero